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diff --git a/.gitattributes b/.gitattributes new file mode 100644 index 0000000..6833f05 --- /dev/null +++ b/.gitattributes @@ -0,0 +1,3 @@ +* text=auto +*.txt text +*.md text diff --git a/18534-8.txt b/18534-8.txt new file mode 100644 index 0000000..8e8078f --- /dev/null +++ b/18534-8.txt @@ -0,0 +1,2238 @@ +The Project Gutenberg EBook of The Hurricane Guide, by William Radcliff Birt + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Hurricane Guide + Being An Attempt To Connect The Rotary Gale Or Revolving + Storm With Atmospheric Waves. + +Author: William Radcliff Birt + +Release Date: June 8, 2006 [EBook #18534] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE HURRICANE GUIDE *** + + + + +Produced by Carlos Traversi, Janet Blenkinship, and the +Online Distributed Proofreaders Europe at +http://dp.rastko.net + + + + + + + + + + + THE + + HURRICANE GUIDE: + + + BEING + + AN ATTEMPT TO CONNECT THE + + ROTATORY GALE OR REVOLVING STORM + + WITH + + ATMOSPHERIC WAVES. + + INCLUDING INSTRUCTIONS FOR OBSERVING THE PHÆNOMENA OF THE WAVES AND + STORMS; + + + WITH + + PRACTICAL DIRECTIONS FOR AVOIDING THE CENTRES OF THE LATTER. + + BY + + WILLIAM RADCLIFF BIRT. + + + LONDON: JOHN MURRAY, ALBEMARLE STREET. + _PUBLISHER TO THE ADMIRALTY._ + 1850. + + PRINTED BY W. CLOWES AND SONS, STAMFORD STREET. + + + + +PREFACE. + + +In introducing the following pages to the notice of the Public, it is +the Author's wish to exhibit in as clear a light as our present +researches on the subjects treated of will allow, the connexion between +one of the most terrific phænomena with which our globe is visited, and +a phænomenon which, although but little known, appears to be intimately +connected with revolving storms. How far he has succeeded, either in +this particular object or in endeavouring to render the essential +phænomena of storms familiar to the seaman, is left for the Public to +determine. Should any advantage be found to result from the study of the +Atmospheric Waves, as explained and recommended in this little work, or +the seaman be induced by its perusal to attend more closely to the +observations of those instruments that are calculated to warn him of his +danger, an object will be attained strikingly illustrative of the +Baconian aphorism, "Knowledge is Power." + + _Bethnal Green_, April 19, 1849. + + + + + CONTENTS. + + + PAGE + + CHAP. I.--PHÆNOMENA OF REVOLVING STORMS 7 + + " II.--PHÆNOMENA OF ATMOSPHERIC WAVES 13 + + " III.--OBSERVATIONS 18 + + SECT. I.--Instruments 19 + + " II.--Times of Observation 28 + + " III.--Localities for Additional Observations 31 + + " IV.--Storms, Hurricanes, and Typhoons 43 + + " V.--Seasons for Extra Observations 48 + + " IV.--PRACTICAL DIRECTIONS FOR AVOIDING THE CENTRES + OF STORMS 52 + + + + +NOTICE. + + +In the pocket accompanying this work are two rings of stiff cardboard, +on which will be found all the information contained in figures 1 and 2. +When they are laid flatly upon a chart, the continuity of the lines on +the chart is not materially interfered with, while the idea of a body of +air rotating in the direction indicated by the arrows is conspicuously +presented to the mind. These rings are more particularly referred to on +page 52. + + + + +THE + +HURRICANE GUIDE. + + + + + +CHAPTER I. + +PHÆNOMENA OF REVOLVING STORMS. + + +It is the object of the following pages to exhibit, so far as +observation may enable us, and in as brief a manner as possible, the +connexion, if any, that exists between those terrific meteorological +phænomena known as "revolving storms," and those more extensive and +occult but not less important phænomena, "atmospheric waves." + +To the great body of our seamen, whether in her Majesty's or the +mercantile service, the subject can present none other than the most +interesting features. The laws that govern the transmission of large +bodies of air from one part of the oceanic surface to another, either in +a state of rapid rotation or presenting a more or less rectilineal +direction, must at all times form an important matter of inquiry, and +bear very materially on the successful prosecution of the occupation of +the voyager. + +In order to place the subjects above alluded to in such a point of view +that the connexion between them may be readily seen, it will be +important to notice the principal phænomena presented by each. Without +going over the ground so well occupied by those able writers on the +subject of storms--Redfield, Reid, Piddington, and Thom--it will be +quite sufficient for our present purpose simply to notice the essential +phænomena of revolving storms as manifested by the barometer and vane. +The usual indications of a storm in connexion with these instruments are +the _falling_ of the barometer and the _freshening_ of the wind, and it +is generally considered that a _rapid_ fall of the mercury in the +hurricane regions invariably precedes the setting in of a storm. + +There are three classes of phænomena that present themselves to an +observer, according as he is situated _on_ the line or axis of +translation, or _in_ either the right or left hand semicircle of the +storm. These will be rendered very apparent by a little attention to the +annexed engraving, fig. 1. + +[Illustration: Compass rose] + +In this figure the arrow-head is supposed to be directed true north, and +the hurricane--as is the case in the American storms north of the 30th +parallel--to be moving towards the N.E. on the line N.E.--S.W. If the +ship take the hurricane with the wind S.E.,--the letters within the two +larger circles indicating _the direction of the wind in the storm_ +according to the rotation as shown by the circle of arrow-heads, and +which it is to be particularly noted is in the northern hemisphere +_contrary to the direction in which the hands of a watch move_: in the +southern hemisphere the rotation is reversed--the only phænomena +presented by the storm are as follows:--The wind continues to blow from +the S.E., increasing considerably in force with the barometer falling to +a very great extent until the centre of the storm reaches the ship, when +the fury of the winds is hushed, and a lull or calm takes place, +generally for about half an hour, after which the wind springs up mostly +with increased violence, but from the opposite quarter N.W., the +barometer begins to rise, and as the storm passes off, the force of the +wind abates. + +The point to which we wish particularly to direct attention in connexion +with this exposition of the phænomena attending the transmission of a +storm is this:--If the observer so place himself at the commencement +that the wind passes _from his left hand towards his right_, his face +will be directed towards the centre of the storm; and the wind +undergoing no change in direction, but only in force, will acquaint him +with this important fact that the _centre_ is not only gradually but +surely approaching him: in other words, in the case before us, when he +finds the wind from the S.E., and he places himself with his face to the +S.W. he is looking towards the centre, and the wind rushes past him +_from his left to his right hand_. Now the connexion of the barometer +with this phase of the storm is _falling with the wind from left to +right, the observer facing the centre while the first half is +transiting_.[1] During the latter half these conditions are reversed, +the observer still keeping his position, his face directed to the S.W., +the barometer _rises_ with a N.W. wind, which rushes past him _from his +right to his left hand_ with a decreasing force. We have therefore _a +rising barometer with the wind from right to left during the latter half +of the storm, the observer having his back to the centre_. + +The above _general_ enunciations of the barometric and anemonal +phænomena of a rotating storm hold good with regard to the _northern_ +hemisphere, whatever may be the direction in which the hurricanes +advance. This may be placed in a clearer light, as well as the remaining +classes of phænomena shown, by consulting the following tables, +constructed for the basin of the Northern Atlantic, and comparing them +with fig. 1. In this basin, with lower latitudes than 25°, the usual +paths of the hurricanes are towards the north-west, in higher latitudes +than 30° towards the north-east. The tables exhibit the veering of the +wind with the movements of the barometer, according as the ship is +situated in the right or left hand semicircle of the hurricane. It must +here be understood that the right and left hand semicircles are +determined by the observer so placing himself that his face is directed +towards the quarter to which the hurricane is advancing. + + +LOWER LATITUDES. + +NORTHERN HEMISPHERE. + + Axis line, wind N.E., barometer falling, first half of storm. + Axis line, wind S.W., barometer rising, last half of storm. + +RIGHT-HAND SEMICIRCLE. + + Wind E.N.E., E., E.S.E., S.E., barometer falling, storm increasing. + Wind S.S.W., S., S.S.E., S.E., barometer rising, storm passing off. + +LEFT-HAND SEMICIRCLE. + + Wind N.N.E., N., N.N.W., N.W., barometer falling, storm increasing. + Wind W.S.W., W., W.N.W., N.W., barometer rising, storm passing off. + + +HIGHER LATITUDES. + +NORTHERN HEMISPHERE.[2] + + Axis line, wind S.E., barometer falling, first half of storm. + Axis line, wind N.W., barometer rising, last half of storm. + +RIGHT-HAND SEMICIRCLE. + + Wind S.S.E., S., S.S.W., S.W., barometer falling, storm increasing. + Wind W.N.W., W., W.S.W., S.W., barometer rising, storm passing off. + +LEFT-HAND SEMICIRCLE. + + Wind E.S.E., E., E.N.E., N.E., barometer falling, storm increasing. + Wind N.N.W., N., N.N.E., N.E., barometer rising, storm passing off. + +N.B. The directions of the hurricane winds are so arranged as to show +the points of commencement and termination. Thus in the lower latitudes +a storm commencing at E.N.E. passes off at S.S.W. after the wind has +veered E., E.S.E., S.E., S.S.E., and S., being in the order of the +letters in the upper line and contrary to their order in the lower. One +commencing at E.S.E. passes off at S.S.E. right-hand semicircle. In the +higher latitudes a ship taking the storm at E.N.E. will be in the +left-hand semicircle, and the hurricane will pass off at N.N.E. These +changes are rendered very apparent by moving the hurricane circle in the +direction in which the storm is expected to proceed. + +Fig. 2 represents the whirl and hurricane winds in the south. + +[Illustration: Fig. 2] + + + + +CHAPTER II. + +PHÆNOMENA OF ATMOSPHERIC WAVES. + + +Professor Dove of Berlin has suggested that in the temperate zones the +compensating currents of the atmosphere necessary to preserve its +equilibrium may be arranged as parallel currents on the _surface_, and +not superposed as in or near the torrid zone. His views may be thus +enunciated:--That in the parallels of central Europe the N.E. current +flowing towards the equator to feed the ascending column of heated air +is not compensated by a current in the upper regions of the atmosphere +flowing from the S.W. as in the border of the torrid zone, but there are +also S.W. currents on each side the N.E., which to the various countries +over which they pass appear as surface-winds, the winds in fact being +disposed in alternate beds or layers, S.W., N.E., as in fig. 3. + +[Illustration: Fig. 3.] + +The Professor also suggests that these parallel and oppositely directed +winds are shifting, _i. e._ they gradually change their position with a +lateral motion in the direction of the large arrow cutting them +transversely. + +In the course of the author's researches on atmospheric waves he had an +opportunity of testing the correctness of Professor Dove's suggestion, +and in addition ascertained that there existed another set of oppositely +directed winds at right angles to those supposed to exist by the +Professor. These currents were N.W. and S.E. with a lateral motion +towards the N.E. He also carefully discussed the barometric phænomena +with relation to both these sets of currents, and arrived at the +following conclusions. The details will be found in the author's third +report, presented to the British Association for the Advancement of +Science (Reports, 1846, pp. 132 to 162). During the period under +examination the author found the barometer generally to rise with N.E. +and N.W. winds, and fall with S.W. and S.E. winds, and that the +phænomena might be thus illustrated:--Let the strata _a a a' a', b' b' b +b_, fig. 3, represent two parallel aërial currents or winds, _a a a' a'_ +from S.W. or S.E., and _b' b' b b_ from N.E. or N.W. and conceive them +both to advance from the N.W. in the first instance and from the S.W. in +the second, in the direction of the large arrow. Now conceive the +barometer to commence rising just as the edge _b b_ passes any line of +country, and to continue rising until the edge _b' b'_ arrives at that +line, when the maximum is attained. It will be remarked that this rise +is coincident with a N.E. or N.W. wind. The wind now changes and the +barometer begins to fall, and continues falling until the edge _a a_ +coincides with the line of country on which _b b_ first impinged. +During this process we have all the phænomena exhibited by an +atmospheric wave: when the edge _b b_ passes a line of country the +barometer is at a _minimum_, and this minimum has been termed the +_anterior trough_. During the period the stratum _b' b' b b_ transits, +the barometer rises, and this rise has been called the _anterior slope_. +When the conterminous edges of the strata _a' a' b' b'_ pass, a +barometric _maximum_ extends along the line of country formerly occupied +by the anterior trough, and this maximum has been designated the +_crest_. During the transit of the stratum _a' a' a a_ the barometer +_falls_, and this fall has been characterised as the _posterior slope_; +and when the edge _a a_ occupies the place of _b b_, the descent of the +mercurial column is completed, another _minimum_ extends in the +direction of the former, and this minimum has been termed the _posterior +trough_. + +It will be readily seen that the lateral passage of the N.W. and S.E. +currents towards the N.E. presents precisely the same barometric and +anemonal phænomena as the rotatory storms when moving in the same +direction. If the observer, when the barometer is at a _maximum_ with a +N.W. wind, place himself in the same position with regard to the +laterally advancing current as he did with regard to the advancing +storm, _i. e._ with his face _towards_ the quarter from which it is +advancing--S.W., he will find that with a _falling barometer and S.E. +wind the current passes him from the left to the right hand_; but if at +a barometric _minimum_ he place himself in the same position with his +face directed to the quarter from which the N.W. current is advancing +laterally, also S.W., he will find that with a rising barometer _and +N.W. wind the current passes him from right to left_. Now the two +classes of phænomena are identical, and it would not be difficult to +show that, had we an instance of a rotatory storm in the northern +hemisphere moving from N.W. to S.E., it would present precisely the same +phænomena as to the direction of currents passing from left to right and +from right to left with falling and rising barometers, increase and +decrease in the force of the wind, &c., as the oppositely directed +aërial currents do which pass over western central Europe. + +In the absence of direct evidence of the production of a revolving storm +from the crossing of two large waves, as suggested by Sir John Herschel, +although it is not difficult to obtain such evidence, especially from +the surface of the ocean, the identity of the two classes of phænomena +exhibited by the storms and waves as above explained amounts to a strong +presumption that there is a close connexion between them, and that a +more minute investigation of the phænomena of atmospheric waves is +greatly calculated to throw considerable light on the laws that govern +the storm paths in both hemispheres. The localities in which these +atmospheric movements, the waves, have been hitherto studied, have been +confined to the northern and central parts of Europe--the west of +Ireland, Alten in the north of Europe, Lougan near the Sea of Azov, and +Geneva, being the angular points of the included area. It will be +remarked that the greatest portion of this area is _inland_, but there +is one important feature which the study of the barometer has brought to +light, and which is by no means devoid of significance, viz. that the +oscillations are much greater in the neighbourhood of _water_, and this +appears to indicate that the junction lines of land and water form by +far the most important portions of the globe in which to study both the +phænomena of storms and waves. It is also very desirable that our +knowledge of these phænomena should, with immediate reference to the +surface of the ocean, be increased, and in this respect captains and +masters of vessels may render essential service by observing and +recording the state of the barometer, and direction and force of the +wind, several times in the course of the day and night;[3] and when it +is considered that the immediate object in view is one in which the +mariner is personally interested, and one in which, it may be, his own +safety is concerned, it is hoped that the keeping of a meteorological +register having especial reference to the indications of the barometer, +and force and direction of the wind, will not be felt as irksome, but +rather will be found an interesting occupation, the instruments standing +in the place of faithful monitors, directing when and where to avoid +danger, and the record furnishing important data whereby the knowledge +of general laws may be arrived at, having an essential bearing on the +interests of the service at large. + + + + +CHAPTER III. + +OBSERVATIONS. + + +In sketching out a system of observation having especial reference to +atmospheric waves and rotatory storms, regard has been had--_first_, to +the instruments that should be used, the observations to be made with +them, the corrections to be applied to such observations, and the form +of registry most suitable for recording the results: _second_, to the +times of observation: _third_, to the more important localities that +should be submitted to additional observation: _fourth_, to peculiar +phænomena requiring extraordinary observations for their elucidation: +and _fifth_, to particular seasons, when the instruments should be +watched with more than ordinary care. + +The more important objects of observation having especial reference to +atmospheric waves are those points which have been termed _crests_ and +_troughs_. These are simply the _highest_ and _lowest_ readings of the +barometer, usually designated _maxima_ and _minima_, and should for the +object in view receive particular attention. Whenever there is reason to +believe that the barometer is approaching either a _maximum_ or +_minimum_, additional observations should be resorted to, so as to +secure as nearly as possible _the precise time_ as reckoned at the ship, +with her position, of its occurrence, as well as the altitude of the +mercurial column at that time and place. By means of such observations +as these on board several ships scattered over the surfaces of our great +oceans, much valuable information may be accumulated of a character +capable of throwing considerable light on the _direction_ in which the +lines of barometric maxima and minima stretch, and also a tolerably +accurate notion may be formed of their progress, both as regards +direction and rate. In immediate connexion with such observations +particular attention should be paid to the direction of the wind +according to the season. + + +SECTION I.--INSTRUMENTS. + +_Description and Position of Instruments._--The principal instrument +requisite in these observations is the barometer, which should be of the +marine construction, and as nearly alike as possible to those furnished +to the Antarctic expedition which sailed under the command of Sir James +Clark Ross. These instruments were similar to the ordinary portable +barometers, and differed from them only in the mode of their suspension +and the necessary contraction of the tubes to prevent oscillation from +the motion of the ship. The barometer on shipboard should be suspended +on a gimbal frame, which ought not to swing too freely, but rather so as +to deaden oscillations by some degree of friction. To the upper portion +of the tube in this construction of instrument light is alike accessible +either in front or behind, and the vernier is furnished with a back and +front edge, both being in precisely the same plane, nearly embracing the +tube, and sliding up and down it by the motion of rack-work; by the +graduation of the scale and vernier the altitude of the mercury can be +read off to ·002 inch. + +When the barometer is placed in the ship, its position should be as near +midships as possible, out of the reach of sunshine, but in a good light +for reading, and in a situation in which it will be but little liable to +sudden gusts of wind and changes of temperature. Great care should be +taken to ascertain the exact height of its cistern above the water-line, +and in order to facilitate night observations every possible arrangement +should be made for placing behind it a light screened by white paper. + +_Observations._--The first thing to be done is the reading off and +recording the temperature indicated by the thermometer that in this +construction of instrument dips into the mercury in the cistern. Sir +John Herschel has suggested that "the bulb of the thermometer should be +so situated as to afford the best chance of its indicating the exact +mean of the whole barometric column, that is to say, fifteen inches +above the cistern enclosed within the case of the barometer, nearly in +contact with its tube, and with a stem so long as to be read off at the +upper level." + +Previous to making an observation with the barometer the instrument +should be slightly tapped to free the mercury from any adhesion to the +glass; any violent oscillation should, however, be carefully avoided. +The vernier should then be adjusted to the upper surface of the mercury +in the tube; for this purpose its back and front edges should be made to +coincide, that is, the eye should be placed in exactly the same plane +which passes through the edges; they should then be brought carefully +down until they form a tangent with the curve produced by the convex +surface of the mercury and the light is _just_ excluded from between +them and the point of contact. It is desirable in making this adjustment +that the eye should be assisted by a magnifying-glass. The reading of +the scale should then be taken and entered in the column appropriated to +it in the proper form. If the instrument have no tubular or double-edged +index, the eye should be placed carefully at the level of the upper +surface of the mercury and the index of the vernier brought gently down +to the same level so as apparently just to touch the surface, great care +being taken that the eye index and surface of the mercury are all in the +same plane. + +Each observation of the barometer should be accompanied by an +observation of the direction of the wind, which should be noted in the +usual manner in which it is observed at sea. In connexion with the +_direction_ the _force_ of the wind should be recorded in accordance +with the following scale, contrived by Admiral Sir Francis Beaufort:-- + + 0. Calm + 1. Light air or just sufficient to give steerage way. + 2. Light breeze { or that in which a well- } 1 to 2 knots. + 3. Gentle breeze { conditioned man of war, } 3 to 4 knots. + 4. Moderate breeze { with all sail set, and } 5 to 6 knots. + { clean full, would go in } + { smooth water, from } + 5. Fresh breeze } { Royals, &c. + 6. Strong breeze } { Single-reefed top-sails + } { and top-gallant + } or that in which such a { sails. + 7. Moderate gale } ship could just carry in { Double-reefed + } chase full and by { topsails, jib, &c. + 8. Fresh gale } { Triple-reefed + } { topsails, &c. + 9. Strong gale } { Close-reefed top-sails + } { and courses. + + 10. Whole gale or that with which she could scarcely bear + close-reefed main topsail and reefed foresail. + 11. Storm or that which reduces her to storm staysails. + 12. Hurricane or that which no canvas could withstand. + +_Corrections._--As soon after the observations have been made as +circumstances will permit, the reading of the barometer should be +_corrected_ for the relation existing between the capacities of the tube +and cistern (if its construction be such as to require that correction), +and for the capillary action of the tube; and then _reduced_ to the +standard temperature of 32° Fahr., and to the sea-level, if on +shipboard. For the first correction the _neutral point_ should be marked +upon each instrument. It is that particular height which, in its +construction, has been actually measured from the surface of the mercury +in the cistern, and indicated by the scale. In general the mercury will +stand either above or below the neutral point; if _above_, a portion of +the mercury must have left the cistern, and consequently must have +_lowered_ the surface in the cistern: in this case the altitude as +measured by the scale will be _too short--vice versâ_, if below. The +relation of the capacities of the tube and cistern should be +experimentally ascertained, and marked upon the instrument by the maker. +Suppose the capacity to be 1/50, marked thus on the instrument, +"_Capacity 1/50:_" this indicates that for every inch of variation of +the mercury in the tube, that in the cistern will vary contrariwise +1/50th of an inch. When the mercury in the tube is _above_ the neutral +point, the difference between it and the neutral point is to be reduced +in the proportion expressed by the "capacity" (in the case supposed, +divided by 50), and the quotient _added_ to the observed height; if +_below, subtracted_ from it. In barometers furnished with a fiducial +point for adjusting the lower level, this correction is superfluous, and +must not be applied. + +The second correction required is for the capillary action of the tube, +the effect of which is always to depress the mercury in the tube by a +certain quantity inversely proportioned to the diameter of the tube. +This quantity should be experimentally determined during the +construction of the instrument, and its amount marked upon it by the +maker, and is always to be _added_ to the height of the mercurial +column, previously corrected as before. For the convenience of those who +may have barometers, the capillary action of which has not been +determined, a table of corrections for tubes of different diameters is +placed in the Appendix, Table I. + +The next correction, and in some respects the most important of all, is +that due to the temperature of the mercury in the barometer tube at the +time of observation, and to the expansion of the scale. Table II. of the +Appendix gives for every degree of the thermometer and every half-inch +of the barometer, the proper quantity to be added or subtracted for the +reduction of the observed height to the standard temperature of the +mercury at 32° Fahr. + +After these the index correction should be applied. This is the amount +of difference between the particular instrument and the readings of the +Royal Society's flint-glass barometer when properly corrected, and is +generally known as the _zero_. It is impossible to pay too much +attention to the determination of this point. For this purpose, when +practicable, the instrument should be immediately compared with the +Royal Society's standard, and the difference of the readings of both +instruments, when corrected as above, carefully noted and preserved. +Where, however, this is impracticable, the comparison should be effected +by means either of some other standard previously so compared, or of an +intermediate portable barometer, the zero point of which has been _well +determined_. Suspend the portable barometer as near as convenient to the +ship's barometer, and after at least an hour's quiet exposure, take as +many readings of both instruments as may be necessary to reduce the +probable error of the mean of the differences below 0.001 inch. Under +these circumstances the mean difference of all the readings will be the +_relative_ zero or index error, whence, if that of the intermediate +barometer be known, that of the other may be found. As such comparisons +will always be made when the vessel is in port, sufficient time can be +allowed for making the requisite number of observations: hourly readings +would perhaps be best, and they would have the advantage of forming part +of the system when in operation, and might be accordingly used as such. + +It is not only desirable that the zero point of the barometer should be +well determined in the first instance; it should also be carefully +verified on every opportunity which presents itself; and in every +instance, previous to sailing, it should be re-compared with the +standard on shore by the intervention of a portable barometer, and no +opportunity should be lost of comparing it on the voyage by means of +such an intermediate instrument with the standard barometers at St. +Helena, the Cape of Good Hope, Bombay, Madras, Paramatta, Van Diemen's +Island, and with any other instruments likely to be referred to as +standards, or employed in research elsewhere. Any vessel having a +portable barometer on board, the zero of which has been well determined, +would do well, on touching at any of the ports above named, to take +comparative readings with the standards at those ports, and record the +differences between the standard, the portable, and the ship barometers. +By such means the zero of one standard may be transported over the whole +world, and those of others compared with it ascertained. To do so, +however, with perfect effect, will require that the utmost care should +be taken of the portable barometer; it should be guarded as much as +possible from all accident, and should be kept safely in the "portable" +state when not immediately used for comparison. To transport a +well-authenticated zero from place to place is by no means a point of +trifling importance. Neither should it be executed hurriedly nor +negligently. Some of the greatest questions in meteorology depend on its +due execution, and the objects for which these instructions have been +prepared will be greatly advanced by the zero points of all barometers +being referred to one common standard. Upon the arrival of the vessel in +England, at the termination of the voyage, the ship's barometer should +be again compared with the same standard with which it was compared +previous to sailing; and should any difference be found, it should be +most carefully recorded. + +The correction for the height of the cistern _above_ or _below_ the +water-line is _additive_ in the former case, _subtractive_ in the +latter. Its amount may be taken, nearly enough, by allowing 0·001 in. of +the barometer for each foot of difference of level. + +An example of the application of these several corrections is +subjoined:-- + + + | _Attached Therm_. 54°·3. |_Data for the correction of | + | | the Instrument_. | + +---------------------------------------+-------------------------------+ + |Barometer reading. 29·409 |Neutral point 30·123 | + |Corr. for capacity - ·017 |Capacity 1/42 | + | |Capillary action + ·032 | + +---------------------------------------| | + | 29·392 |Zero to Royal Society + ·036 | + |Corr. for capillarity + ·032 |Corr. for altitude above | + | | water-line + ·004 | + +---------------------------------------| | + | 29·424 | | + |Corr. for temperature - ·068 | | + +---------------------------------------| | + | 29·356 | | + |Corr. for zero and water-line + ·040 | | + +---------------------------------------| | + |Aggregate = pressure at | | + | sea-level 29·396 | | + +---------------------------------------+-------------------------------+ + + +It would greatly facilitate the comparison of the barometric +observations by projecting them in curves when all the proper +corrections have been applied. This may be accomplished by a much +smaller expenditure of time than may at first be supposed. A paper of +engraved squares on which the observations of twelve days may be laid +down on double the natural scale, would be very suitable for the +purpose.[4] The projection of each day's observations would occupy but a +short time; and should circumstances on any occasion prevent the +execution of it, when the ship was becalmed or leisure otherwise +afforded, it would form an interesting and useful occupation, and serve +to beguile some of the tedium often experienced at such intervals. + +_Registers._--For the particular object in view the register need not be +very extensive. One kept in the annexed form will be amply sufficient. +It should, however, be borne in mind that none but _uncorrected_ +observations should find admission; in point of fact it should be +strictly a register of phænomena as _observed_, and on no account +whatever should any entry be made from recollection, or any attempt made +to fill up a blank by the apparent course of the numbers before and +after. The headings of the columns will, it is hoped, be sufficiently +explicit. It is desirable in practice that the column for remarks should +embrace an entire page opposite the other entries, in order that +occasional observations, as well as several other circumstances +continually coming under review in the course of keeping a journal, may +find entry. + +METEOROLOGICAL REGISTER kept on board ______ during her voyage from + ______ to ______ by ______. + + +---------+----+------+-------+------+------------------+--------+----------+ + | | | | | | Wind. | | | + | | | | | Att. |-----------+------| | | + | Date. |Lat.| Long.| Barom.| Ther.| Direction.|Force.| Remarks| Observer.| + |---------|----|------|-------|------|-----------|------|--------|----------| + | |h. m.| | | | | | | | | + | | | | | | | | | | | + | | | | | | | | | | | + | | | | | | | | | | | + | | | | | | | | | | | + | | | | | | | | | | | + +---+-----+----+------+-------+------+-----------+------+--------+----------+ + +The only difference between the above form and one for the reception of +_corrected_ readings will be the dispensing with the column for the +attached thermometer, and placing under the word Barom. "corrected." + + +II.--TIMES OF OBSERVATION. + +There can be no question that the greatest amount of information, the +accuracy of the data supplied, and in fact every meteorological element +necessary to increase our knowledge of atmospheric waves, may be best +obtained by an uninterrupted series of _hourly_ observations made on +board vessels from their leaving England until their safe arrival again +at the close of their respective voyages; but from a variety of +circumstances--the nature of the service in which the vessels may be +employed, particular states of the weather, &c.--such a course of +unremitting labour cannot be expected; it is therefore necessary to fix +on some stated hours at which the instruments before particularized +should be regularly observed throughout the voyage, and their +indications faithfully recorded. The hours of 3 A.M., 9 A.M., 3 P.M., +and 9 P.M., are now so generally known as _meteorological hours_, that +nothing should justify a departure from them; and it is the more +essential that these hours should be adopted in the present inquiry, +because the series of observations made at intervals terminated by these +hours can the more readily be used in connexion with those made +contemporaneously on land, and will also serve to carry on +investigations previously instituted, and which have received +considerable illustration by means of observations at the regular +meteorological hours; we therefore recommend their general adoption in +all observations conducted at sea. + +It is intended in the sequel to call attention to particular parts of +the earth's surface where it is desirable that additional observations +should be made, in order to furnish data of a more accurate character, +and to mark more distinctly barometric changes than the four daily +readings are capable of effecting. The best means of accomplishing this +for the object in view appears to be the division of the interval of six +hours into two equal portions, and to make the necessary observations +eight times in the course of twenty-four hours. In the particular +localities to which allusion has been made we recommend the following as +the hours of observation:-- + +A.M. 3, 6, 9, noon. P.M. 3, 6, 9, midnight. + +In other localities besides those hereafter to be mentioned, when +opportunities serve, readings at these hours would greatly enhance the +value of the four daily readings. + +There are, however, portions of the surface of our planet, and probably +also phænomena that occur in its atmosphere, which require still closer +attention than the eight daily readings. One such portion would appear +to exist off the western coast of Africa, and we recommend the adoption +of _hourly_ readings while sailing to the westward of this junction of +aqueous and terrestrial surface; more attention will be directed to this +point as we proceed. There are also phænomena the localities of which +may be undetermined, and the times of their occurrence unknown, but so +important a relation do they bear to the subject of our inquiries, that +they demand the closest attention. They will be more particularly +described under the head of accumulations of pressure preceding and +succeeding storms, and minute directions given for the hourly +observations of the necessary instruments. In the mean time we may here +remark that hourly observations under the circumstances above alluded to +are the more important when we consider that the barometer, the +instrument employed in observing these moving atmospheric masses, is +itself in motion. The ship may meet the accumulation of pressure and +sail through it transversely; or she may sail along it, the course of +the vessel being parallel to the line marking the highest pressure, the +ridge or crest of the wave; or the ship may make any angle with this +line: but whatever the circumstances may be under which she passes +through or along with such an accumulation of pressure, it should ever +be borne in mind that her position on the earth's surface is scarcely +ever the same at any one observation as it was at the preceding, the +barometer in the interval has changed _its_ position as well as the line +of maximum pressure, the rate of progress of which it is desirable to +observe. It will, therefore, be at once apparent that in order to obtain +the most accurate data on this head hourly observations are +indispensable. To these readings should of course be appended the places +of the ship from hour to hour, especially if she alter her course much. + +There is another point to which we wish to call attention in immediate +connexion with hourly readings--it is the observation of the instruments +on the days fixed for that purpose: they were originally suggested by +Sir John Herschel, whose directions should be strictly attended to: they +are as follows:-- + +The days fixed upon for these observations are the 21st of March, the +21st of June, the 21st of September, and the 21st of December, being +those, or immediately adjoining to those of the equinoxes and +solstices, in which the _solar influence_ is either stationary or in a +state of most rapid variation. _But should any one of those 21st days +fall on a Sunday, then it will be understood that the observations are +to be deferred till the next day, the 22nd._ The series of observations +on board each vessel should commence at 6 o'clock A.M. of the appointed +days, and terminate at 6 A.M. of the days following, according to the +usual reckoning of time adopted in the daily observations. + +In addition to the twenty-five hourly readings at the solstices and +equinoxes as above recommended, it would be desirable to continue the +observations until a complete elevation and depression of the barometer +had been observed at these seasons. This plan is adopted at the Royal +Observatory, Greenwich, and would be attended with this advantage were +it generally so--the progress of the elevation and depression would be +more readily traced and their velocities more accurately determined than +from the four or eight daily readings. + + +III.--LOCALITIES FOR ADDITIONAL OBSERVATIONS. + +In sketching out a system of barometric observation having especial +reference to the acquisition of data from which the _barometric +character_ of certain large areas of the surface of the globe may be +determined--inasmuch as such areas are distinguished from each other, on +the one hand by consisting of extensive spaces of the oceanic surface +unbroken, or scarcely broken, by land; on the other by the proximity of +such oceanic surface to large masses of land, and these masses +presenting two essentially different features, the one consisting of +land particularly characterized as continental, the other as insular, +regard has been accordingly had to such distribution of land and water. + +As these instructions have especial reference to observations at sea, +observations on land have not been alluded to; but in order that the +data accumulated may possess that value which is essential for carrying +on the inquiry in reference to atmospheric waves with success, provision +is made to mark out more distinctly the barometric effects of the +junction of large masses of land and water. It is well known that the +oceanic surface, and even the smaller surfaces of inland seas, produce +decided inflexions of the isothermal lines. They exercise an important +influence on temperature. It has also been shown that the neighbourhood +of water has a very considerable influence in increasing the +oscillations of the mercurial column in the barometer, and in the great +systems of European undulations it is well known that these oscillations +increase especially towards the north-west. The converse of this, +however, has not yet been subjected to observation; there has been no +systematic co-operation of observers for the purpose of determining the +barometric affections of large masses of water, such as the central +portion of the basin of the northern Atlantic, the portion of oceanic +surface between the Cape of Good Hope and Cape Horn, the Indian and +Southern oceans, and the vast basin of the Pacific. Nor are we yet +acquainted with the character of the oscillations, whether increasing or +decreasing, as we recede from the central portions of the oceanic +surfaces we have mentioned towards the land which forms their eastern, +western, or northern boundaries. This influence of the junction line of +land and water, so far as it is yet known, has been kept in view in +framing these instructions, and, as it appears so prominently in Europe, +it is hoped the additional observations between the four daily readings +to which probably many observers may habitually restrict themselves, +making on certain occasions and in particular localities a series of +observations at intervals of three hours, will not be considered too +frequent when the great importance of the problem to be solved is fully +apprehended. It need scarcely be said that the value of these +observations at three-hourly intervals will be greatly increased by the +number of observers co-operating in them. Upon such an extensive system +of co-operation a large space on the earth's surface, possessing +peculiarities which distinguish it from others extremely unlike it in +their general character, or assimilate it to such as possess with it +many features in common, is marked out below for particular observation, +occupying more than two-thirds of a zone in the northern hemisphere, +having a breadth of 40°, and including every possible variety of +terrestrial and aqueous surface, from the burning sands of the great +African desert, situated about the centre, to the narrow strip of land +connecting the two Americas on the one side, and the chain of islands +connecting China and Hindostan with Australia on the other. On each side +of the African continent we have spaces of open sea between 30° and 40° +west longitude north of the equator, and between 60° and 80° east +longitude, in or to the south of the equator, admirably suited for +contrasting the barometric affections, as manifested in these spaces of +open water, with those occurring in situations where the influence of +the terrestrial surface comes into more active operation. + +The localities where three-hourly readings are chiefly desirable may be +specified under the heads of _Northern Atlantic, Southern Atlantic, +Indian_ and _Southern Oceans,_ and _Pacific Ocean_. + + +_Northern Atlantic. Homeward-bound Voyages._--The discussion of +observations made in the United Kingdom and the western border of +central Europe, has indicated that off the north-west of Scotland a +centre of great barometric disturbance exists. This centre of +disturbance appears to be considerably removed from the usual tracks of +vessels crossing the Atlantic; nevertheless some light may be thrown on +the barometric phænomena resulting from this disturbance by observations +during homeward-bound voyages, especially after the vessels have passed +the meridian of 50° west longitude. Voyagers to or from Baffin and +Hudson bays would do well during the whole of the voyage to read off the +barometer every three hours, as their tracks would approach nearest the +centre of disturbance in question. Before crossing the 50th meridian, +the undulations arising from the distribution of land and water in the +neighbourhood of these vast inland seas would receive considerable +elucidation from the shorter intervals of observation, and after passing +the 50th meridian the extent of undulation, as compared with that +observed by the more southerly vessels, would be more distinctly marked +by the three-hourly series. Surveying vessels stationed on the +north-western coasts of Ireland and Scotland may contribute most +important information on this head by a regular and, as far as +circumstances will allow, an uninterrupted series either of six-hourly +or three-hourly observations. The intervals of observation on board +vessels stationed at the Western Isles, the Orkneys, and the Shetland +Isles, ought not to be longer than _three_ hours, principally on account +of the great extent of oscillation observed in those localities. Vessels +arriving from all parts of the world as they approach the United Kingdom +should observe at shorter intervals than six hours. As a general +instruction on this head the series of three-hourly observations may be +commenced on board vessels from America and the Pacific by the way of +Cape Horn on their passing the 20th meridian, such three-hourly +observations to be continued until the arrival of the vessels in port. +Ships by the way of the Cape of Good Hope should commence the +three-hourly series either on leaving or passing the colony, in order +that the phænomena of the tropical depression hereafter to be noticed +may be well observed. + + +_Northern Atlantic. Outward-bound Voyages_.--Vessels sailing to the +United States, Mexico, and the West Indies, should observe at three +hours' interval upon passing the 60th meridian. Observations at this +interval, on board vessels navigating the Gulf of Mexico and the +Caribbean Sea, will be particularly valuable in determining the extent +of oscillation as influenced by the masses of land and water in this +portion of the torrid zone, as compared with the oscillation noticed off +the western coast of Africa, hereafter to be referred to. + + +_Southern Atlantic. Outward and homeward bound_.--Without doubt the most +interesting phænomenon, and one that lies at the root of the great +atmospheric movements, especially those proceeding northwards in the +northern hemisphere and southwards in the southern, is the equatorial +depression first noticed by Von Humboldt and confirmed by many observers +since. We shall find the general expression of this most important +meteorological fact in the Report of the Committee of Physics and +Meteorology, appointed by the Royal Society in 1840, as follows: "The +barometer, at the level of the sea, does not indicate a mean atmospheric +pressure of equal amount in all parts of the earth; but, on the +contrary, the equatorial pressure is uniformly less in its mean amount +than at and beyond the tropics." Vessels that are outward bound should, +upon passing 40° north latitude, commence the series of three-hourly +observations, with an especial reference to the equatorial depression. +These three-hourly observations should be continued until the latitude +of 40° south has been passed: the whole series will then include the +minimum of the depression and the two maxima or apices forming its +boundaries. (See Daniell's 'Meteorological Essays,' 3rd edition.) In +passages across the equator, should the ships be delayed by calms, +opportunities should be embraced for observing this depression with +greater precision by means of _hourly_ readings; and these readings will +not only be valuable as respects the depression here spoken of, but will +go far to indicate the character of any disturbance that may arise, and +point out, as nearly as such observations will allow, the precise time +when such disturbance produced its effects in the neighbourhood of the +ships. In point of fact they will clearly illustrate the diversion of +the tendency to rise, spoken of in the Report before alluded to, as +resulting in ascending columns and sheets, between which wind flaws, +capricious in their direction and intensity, and often amounting to +sharp squalls, mark out the course of their feeders and the indraft of +cooler air from a distance to supply their void. Hourly observations, +with especial reference to this and the following head of inquiry, +should also be made off the western coast of Africa during the +homeward-bound voyage. + +Immediately connected with this part of the outward-bound voyage, hourly +observations, as often as circumstances will permit, while the ships are +sailing from the Madeiras to the equator, will be extremely valuable in +elucidating the origin of the great system of south-westerly atmospheric +waves that traverse Europe, and in furnishing data for comparison with +the amount of oscillation and other barometric phænomena in the Gulf of +Mexico and the Caribbean Sea, a portion of the torrid zone essentially +different in its configuration and in the relations of its area to land +and water, as contra-distinguished to the northern portion of the +African continent; and these hourly observations are the more desirable +as the vessels may approach the land. They may be discontinued on +passing the equator, and the three-hourly series resumed. + +There are two points in the southern hemisphere, between 80° west +longitude and 30° east longitude, that claim particular attention in a +barometric point of view, viz., Cape Horn and the Cape of Good Hope; the +latter is within the area marked out for the three-hourly observations, +and too much attention cannot be paid to the indications of the +barometer as vessels are approaching or leaving the Cape. The northern +part of the South Atlantic Ocean has been termed the _true Pacific Ocean +of the world_; and at St. Helena a gale was scarcely ever known; it is +also said to be entirely free from actual storms (Col. Reid's 'Law of +Storms,' 1st edition, p. 415). It may therefore be expected that the +barometer will present in this locality but a small oscillation, and +ships in sailing from St. Helena to the Cape will do well to ascertain, +by means of the three-hourly observations, the increase of oscillation +as they approach the Cape. The same thing will hold good with regard to +Cape Horn: it appears from previous observation that a permanent +barometric depression exists in this locality, most probably in some way +connected with the immense depression noticed by Captain Sir James Clark +Ross, towards the Antarctic Circle. The general character of the +atmosphere off Cape Horn is also extremely different from its character +at St. Helena. It would therefore be well for vessels sailing into the +Pacific by Cape Horn, to continue the three-hourly observations until +the 90th meridian is passed. + +Before quitting the Atlantic Ocean it may be well to notice the marine +stations mentioned in my Third Report on Atmospheric Waves,[5] as being +particularly suitable for testing the views advanced in that report and +for tracing a wave of the south-westerly system from the most western +point of Africa to the extreme north of Europe. A series of hourly +observations off the western coast of Africa has already been suggested. +Vessels staying at Cape Verd Islands should not omit to make +observations at three hours' interval _during the whole of their stay_, +and when circumstances will allow, hourly readings. At the Canaries, +Madeiras, and the Azores, similar observations should be made. Vessels +touching at Cape Cantin, Tangier, Gibraltar, Cadiz, Lisbon, Oporto, +Corunna, and Brest, should also make these observations while they are +in the localities of these ports. At the Scilly Isles we have six-hourly +observations, made under the superintendence of the Honourable the +Corporation of the Trinity House. Ships in nearing these islands and +making the observations already pointed out, will greatly assist in +determining the increase of oscillation proceeding westward from the +nodal point of the two great European systems. We have already mentioned +the service surveying vessels employed on the coasts of Ireland and +Scotland may render, and the remaining portion of the area marked out in +the report may be occupied by vessels navigating the North Sea and the +coast of Norway, as far as Hammerfest. + +In connexion with these observations, having especial reference to the +European system of south-westerly atmospheric waves, the Mediterranean +presents a surface of considerable interest, both as regards these +particular waves, and the influence its waters exert in modifying the +two great systems of central Europe. The late Professor Daniell has +shown from the Manheim observations, that small undulations, having +their origin on the northern borders of the Mediterranean, have +propagated themselves northward, and in this manner, but in a smaller +degree, the waters of the Mediterranean have contributed to increase the +oscillation as well as the larger surface of the northern Atlantic. In +most of the localities of this great inland sea six-hourly observations +may suffice for this immediate purpose; but in sailing from Lisbon +through the Straits of Gibraltar, in the neighbourhood of Sicily and +Italy, and in the Grecian Archipelago, we should recommend the +three-hourly series, as marking more distinctly the effects resulting +from the proximity of land; this remark has especial reference to the +passage through the Straits of Gibraltar, where, if possible, hourly +observations should be made. + + +_The Indian and Southern Oceans. Outward and homeward bound._--On +sailing from the Cape of Good Hope to the East Indies, China, or +Australia, observations at intervals of three hours should be made until +the 40th meridian east is passed (homeward-bound vessels should commence +the three-hourly readings on arriving at this meridian). Upon leaving +the 40th meridian the six-hourly observations may be resumed on board +vessels bound for the Indies and China until they arrive at the equator, +when the readings should again be made at intervals of three hours, and +continued until the arrival of the vessels in port. With regard to +vessels bound for Australia and New Zealand, the six-hourly readings may +be continued from the 40th to the 100th meridian, and upon the vessels +passing the latter, the three-hourly readings should be commenced and +continued until the vessels arrive in port. Vessels navigating the +Archipelago between China and New Zealand, should make observations +every three hours, in order that the undulations arising from the +configuration of the terrestrial and oceanic surfaces may be more +distinctly marked and more advantageously compared with the Gulf of +Mexico, the Caribbean Sea, and the northern portion of the African +continent. + + +_The Pacific Ocean._--As this ocean presents so vast an aqueous surface, +generally speaking observations at intervals of six hours will be amply +sufficient to ascertain its leading barometric phænomena. Vessels, +however, on approaching the continents of North and South America, or +sailing across the equator, should resort to the three-hourly readings, +in order to ascertain more distinctly the effect of the neighbourhood of +land on the oscillations of the barometer, as generally observed, over +so immense a surface of water in the one case, and the phænomena of the +equatorial depression in the other: the same remarks relative to the +latter subject, which we offered under the head of South Atlantic, will +equally apply in the present instance. The configuration of the western +shores of North America renders it difficult to determine the precise +boundary where the three-hourly series should commence; the 90th +meridian is recommended for the boundary as regards South America, and +from this a judgment may be formed as to where the three-hourly +observations should commence in reference to North America. + + +In the previous sketch of the localities for the more important +observations, it will be seen that within the tropics there are three +which demand the greatest regard. + +I. The Archipelago between the two Americas, more particularly comprised +within the 40th and 120th meridians west longitude, and the equator and +the 40th degree of north latitude. As a general principle we should say +that vessels within this area should observe the barometer every three +hours. Its eastern portion includes the lower branches of the storm +paths, and on this account is peculiarly interesting, especially in a +barometric point of view. + +II. _The Northern portion of the African Continent, including the Sahara +or Great Desert._--This vast radiating surface must exert considerable +influence on the waters on each side northern Africa. Vessels sailing +within the area comprised between 40° west and 70° east, and the equator +and the 40th parallel, should also make observations at intervals of +three hours. + +III. _The great Eastern Archipelago._--This presents a somewhat similar +character to the western; like that, it is the region of terrific +hurricanes, and it becomes a most interesting object to determine its +barometric phænomena; the three-hourly system of observation may +therefore be resorted to within an area comprised between the 70th and +140th meridians, and the equator and the 40th degree of north latitude. + +The southern hemisphere also presents three important localities, the +prolongations of the three tropical areas. It is unnecessary to enlarge +upon these, as ample instructions have been already given. We may, +however, remark, with regard to Australia, that three-hourly +observations should be made within the area comprised between the 100th +and 190th meridians east, and the equator and the 50th parallel south, +and hourly ones in the immediate neighbourhood of all its coasts. + + +IV.--STORMS, HURRICANES, AND TYPHOONS. + +The solution of the question--How far and in what manner are storms +connected with atmospheric waves?--must be extremely interesting to +every one engaged in either the naval or merchant service. As we have in +the former chapters directed attention to their connexion, our great +object here will be to endeavour to mark out such a line of observation +as appears most capable of throwing light, not only on the most +important desiderata as connected with storms, but also their connexion +or non-connexion with atmospheric waves. We shall accordingly +arrange this portion of the instructions under the following +heads:--_Desiderata_; _Localities_; _Margins_; _Preceding and Succeeding +Accumulations of Pressure._ + +_Desiderata._--The most important desiderata appertaining to the subject +of storms, are certainly their origin and termination. Of these initial +and terminal points in the course of great storms we absolutely know +nothing, unless _the white appearance of a round form_ observed by Mr. +Seymour on board the Judith and Esther, in lat. 17° 19' north and long. +52° 10' west (see Col. Reid's 'Law of Storms,' 1st edit. p. 65), may be +regarded as the commencement of the Antigua hurricane of August 2, 1837. +This vessel was the most eastern of those from which observations had +been obtained; and it is the absence of contemporaneous observations to +the eastward of the 50th meridian that leaves the question as to the +origin of the West Indian revolving storms unsolved. Not one of Mr. +Redfield's storm routes extends eastward of the 50th meridian; this at +once marks out, so far as storms are concerned, the entire space +included between the 20th and 50th meridians, the equator and the 60th +parallel, as a most suitable area for observations, under particular +circumstances hereafter to be noticed, with especial reference either to +the commencement or termination of storms, or the prolongation of Mr. +Redfield's storm paths. + +_Localities._--The three principal localities of storms are as +follows:--I. The western portion of the basin of the North Atlantic; II. +The China Sea and Bay of Bengal; and III. The Indian Ocean, more +particularly in the neighbourhood of Mauritius. The first two have +already been marked out as areas for the three-hourly observations; to +the latter, the remark as to extra observations under the head of +Desiderata will apply. + +_Margins._--Mr. Redfield has shown that on some occasions storms have +been preceded by an unusual pressure of the atmosphere; the barometer +has stood remarkably _high_, and it has hence been inferred that there +has existed _around_ the gale an accumulation of air forming a margin; +barometers placed under this margin indicating a much greater pressure +than the mean of the respective localities. With regard to the West +Indian and American hurricanes--any considerable increase of pressure, +especially within the space marked out to the eastward of the 50th +meridian, will demand immediate attention. Upon the barometer ranging +_very high_ within this space, three-hourly observations should be +immediately resorted to; and if possible, _hourly_ readings taken, and +this is the more important the nearer the vessel may be to the 50th +meridian. Each observation of the barometer should be accompanied by an +observation of the wind--its direction should be most carefully noted, +and the force estimated according to the scale in page 21, or by the +anemometer. It would be as well _at the time_ to project the barometric +readings in a curve even of a rough character, that the extent of fall +after the mercury had passed its maximum might be readily discernible by +the eye. A paper ruled in squares, the vertical lines representing the +commencement of hours, and the horizontal tenths of an inch, would be +quite sufficient for this purpose. The _force_ of the wind should be +noted at, or as near to the time of the passage of the maximum as +possible. During the fall of the mercury particular attention should be +paid to the manner in which the wind changes, should any change be +observed; and should the wind continue blowing steadily in _one_ +direction, but gradually _increasing_ in force, then such increments of +force should be most carefully noted. During the fall of the barometer, +should the changes of the wind and its increasing force indicate the +neighbourhood of a revolving storm, (independent of the obvious reasons +for avoiding the focus of the storm,) it would contribute as much to +increase our knowledge of these dangerous vortices to keep as near as +possible to their margins as to approach their centres. The recess from +the centre towards the margin of the storm, will probably be rendered +apparent by the _rising_ of the mercury; and so far as the observations +may be considered valuable for elucidating the connexion of atmospheric +waves with rotatory storms (other motives being balanced), it might be +desirable to keep the ship near the margin--provided she is not carried +beyond the influence of the winds which characterize the latter half of +the storm--until the barometer has nearly attained its usual elevation. +By this means some notion might be formed of the general direction of +the line of barometric pressure preceding or succeeding a storm. + +Should a gale be observed commencing without its having been preceded by +an unusual elevation of the mercurial column, and consequently no +additional observation have been made; when the force of the wind is +noted in the usual observations at or above 5, then the three-hourly +series should be resorted to, and the same care taken in noting the +direction, changes, and force of the wind as pointed out in the +preceding paragraph. + +The foregoing remarks relate especially to the central and western +portions of the North Atlantic; they will however equally apply to the +remaining localities of storms. Under any circumstances, and in any +locality, a _high_ barometer not less than a low one should demand +particular attention, and if possible, _hourly_ readings taken some time +before and after the passage of the maximum: this will be referred to +more particularly under the next head. + +_Preceding and Succeeding Accumulations of Pressure._--Mr. Redfield has +shown in his Memoir of the Cuba Hurricane of October, 1844, that two +associated storms were immediately preceded by a barometric wave, or +accumulation of pressure, the barometer rising above the usual or annual +mean. We have just referred to the importance of _hourly_ observations +on occasions of the readings being _high_ as capable of illustrating the +marginal phænomena of storms, and in connexion with these accumulations +of pressure in advance of storms we would reiterate the suggestion. +These strips of accumulated pressure are doubtless crests of atmospheric +waves rolling forwards. In some cases a ship in its progress may cut +them transversely in a direction at right angles to their _length_, in +others very obliquely; but in all cases, whatever section may be given +by the curve representing the observations, too much attention cannot be +bestowed on the barometer, the wet and dry bulb thermometer, the +direction and force of the wind, the state of the sky, and the +appearance of the ocean during the ship's passage _through_ such an +accumulation of pressure. When the barometer attains its mean altitude, +and is rapidly rising above it in any locality, then _hourly_ +observations of the instruments and phænomena above noticed should be +commenced and continued until after the mercury had attained its highest +point and had sunk again to its mean state. In such observations +particular attention should be paid to the direction and force of the +wind preceding the barometric maximum--and the same phænomena succeeding +it, and particular notice should be taken of the time when, and amount +of any change either in the direction or force of the wind. It is by +such observations as these, carried on with great care and made at every +accessible portion of the oceanic surface, that we may be able to +ascertain the continuity of these atmospheric waves, to determine +somewhat respecting their length, to show the character of their +connexion with the rotatory storm, and to deduce the direction and rate +of their progress. + + +V.--SEASONS FOR EXTRA OBSERVATIONS. + +In reference to certain desiderata that have presented themselves in the +course of my researches on this subject (see Report of the British +Association for the Advancement of Science, 1846, p. 163), the _phases_ +of the larger barometric undulations, and the _types_ of the various +seasons of the year, demand particular attention and call for extra +observations at certain seasons: of these, three only have yet been +ascertained--the type for the middle of November--the annual depression +on or about the 28th of November--and the annual elevation on or about +the 25th of December. The enunciation of the first is as under: "That +during fourteen days in November, more or less equally disposed about +the middle of the month, the oscillations of the barometer exhibit a +remarkably symmetrical character, that is to say, the fall succeeding +the transit of the maximum or the highest reading is to a great extent +similar to the preceding rise. This rise and fall is not continuous or +unbroken; in some cases it consists of _five_, in others of _three_ +distinct elevations. The complete rise and fall has been termed the +great symmetrical barometric wave of November. At its setting in the +barometer is generally low, sometimes below twenty-nine inches. This +depression is generally succeeded by _two_ well-marked undulations, +varying from one to two days in duration. The central undulation, which +also forms the apex of the great wave, is of larger extent, occupying +from three to five days; when this has passed, two smaller undulations +corresponding to those at the commencement of the wave make their +appearance, and at the close of the last the wave terminates." With but +slight exceptions, the observations of eight successive years have +confirmed the general correctness of this type. On two occasions the +central apex has not been the highest, and these deviations, with some +of a minor character, form the exceptions alluded to. This type only has +reference to London and the south-eastern parts of England; proceeding +westward, north-westward, and northward, the symmetrical character of +this type is considerably departed from; each locality possessing its +own type of the barometric movements during November. The desiderata in +immediate connexion with the November movements, as observed in the +southern and south-eastern parts of England, that present themselves, +are--the determination of the types for November, especially its middle +portion, as exhibited on the oceanic surface within an area comprised +between the 30th and 60th parallels, and the 1st and 40th meridians +west. Vessels sailing within this area may contribute greatly to the +determination of these types by making observations at intervals of +three hours from the 1st of November to the 7th or 8th of December. The +entire period of the great symmetrical wave of November will most +probably be embraced by such a series of observations, as well as the +annual depression of the 28th. For the elevation of the 25th of December +the three-hourly observations should be commenced on the 21st, and +continued until the 3rd or 4th of the succeeding January. + +With respect to the great wave of November, our knowledge of it would be +much increased by such a series of observations as mentioned above, +being made on board surveying and other vessels employed off Scotland +and Ireland; vessels navigating the North Sea; vessels stationed off the +coasts of France, Spain, Portugal, and the northern parts of Africa, and +at all our stations in the Mediterranean. In this way the area of +examination would be greatly enlarged, and the _differences_ of the +curves more fully elucidated; and this extended area of observation is +the more desirable, as there is some reason to believe that the line of +greatest symmetry _revolves_ around a fixed point, most probably the +nodal point of the great European systems. + +It is highly probable that movements of a somewhat similar character, +although presenting very different curves, exist in the southern +hemisphere. The November wave is more or less associated with storms. It +has been generally preceded by a high barometer and succeeded by a low +one, and this low state of the barometer has been accompanied by stormy +weather. We are therefore prepared to seek for similar phænomena in the +southern hemisphere, in those localities which present similar states of +weather, and at seasons when such weather predominates. We have already +marked out the two capes in the Southern hemisphere for three-hourly +observations: they must doubtless possess very peculiar barometric +characters, stretching as they do into the vast area of the Southern +Ocean. It is highly probable that the oscillations, especially at some +seasons, are very considerable, and vessels visiting them at such +seasons would do well to record with especial care the indications of +the instruments already alluded to. At present we know but little of the +barometric movements in the Southern hemisphere, and every addition to +our knowledge in this respect will open the way to more important +conclusions. + +It has been observed in the south-east of England that the barometer has +generally passed a maximum on or about the 3rd of every month, and this +has been so frequently the case as to form the rule rather than the +exception. The same fact during a more limited period has been observed +at Toronto. With especial reference to this subject the three-hourly +series of observations may be resorted to in all localities, but +especially north of the 40th parallel in the northern hemisphere. They +should be commenced at midnight immediately preceding the 1st and +continued to midnight succeeding the 5th. + + + + +CHAPTER IV. + +PRACTICAL DIRECTIONS FOR AVOIDING THE CENTRES OF ROTATING +STORMS. + + +Figures 1 and 2, enlarged and printed on narrow rings of stiff +cardboard, are employed for this purpose. The letters outside the thick +circle are intended to distinguish the points of the compass, and in use +should always coincide with those points on the chart. The letters +within the thick circle indicate the direction of the wind in a +hurricane, the whirl being shown by the arrows between the letters. In +the northern hemisphere the direction of the whirl is always contrary to +that in which the hands of a watch move, and in the southern coincident +thereto. The graduation is intended to assist the mariner in +ascertaining the bearing of the centre of a storm from his ship. + + +_Use._ + +At any time when a severe gale or hurricane is expected, the seaman +should at once find the position of his ship on the chart, and place +upon it the graduated point which answers to the direction of the wind +at the time, taking care that the needle is directed to the north, so +that the exterior letters may point on the chart to the respective +points of the compass: this is very essential. This simple process will +at once acquaint the seaman with two important facts relative to the +coming hurricane--his position in the storm, and the direction in +which it is moving. + + +_Examples._ + +A captain of a ship in latitude 35° 24' N., longitude 64° 12' W., bound +to the United States, observes the barometer to stand unusually high, +say 30·55 inches: shortly after the mercury begins to fall, at first +slowly and steadily; as the glass falls the wind freshens, and is +noticed to blow with increasing force from the S. so as to threaten a +gale. The position of the ship on the chart is now to be found, and the +graduated point under the letters E. S. is to be placed thereon, +taking care to direct the needle to the north. From these two +circumstances, the falling barometer and the wind blowing from the south +with increasing force, the mariner is aware of this simple fact, that he +is situated in the advancing portion of a body of air which is +proceeding towards the N.E.; and if he turn his face to the N.E. he will +find he is on the right of the axis line, or line cutting the advancing +body transversely. The hurricane circle as it lies on the chart reveals +to him another important fact, which is, that if he pursue his course he +will sail _towards_ the axis line of the hurricane, and may stand a +chance of foundering in its centre. To avoid this he has one of two +courses to adopt; either to lay-to on the _starboard tack_, according to +Col. Reid's rules (see his 'Law of Storms,' 1st edit., pp. 425 to 428), +the ship being in the right-hand semicircle of the hurricane, or so to +alter his course as to keep without the influence of the storm. In the +present case the adoption of the latter alternative would involve a +reversal of his former course; nevertheless it is clear the more he +bears to the S.E. the less he will experience the violence of the +hurricane: should he heave his ship to, upon moving the hurricane circle +from the ship's place on the chart towards the N.E., he will be able to +judge of the changes of the wind he is likely to experience: thus it +will first veer to S.S.W., the barometer still falling; then to S.W., +the barometer at a minimum--this marks the position of the most violent +portion of the storm he may be in, and by keeping the barometer as high +as he can by bearing towards the S.E., the farther he will be from the +centre--the barometer now begins to rise, the wind veering to W.S.W., +and the hurricane finally passes off with the wind at W. It is to be +particularly remarked that in this example the ship is in the _most +dangerous quadrant_, as by scudding she would be driven in advance of +the track of the storm's centre, which of course would be approaching +her. + +Assuming that the hurricane sets in at the ship's place with the wind at +S.E., the proceeding will be altogether different. At first the wind is +fair for the prosecution of the voyage, and it is desirable to take +advantage of this fair wind to avoid as much as possible the track of +the centre, which passes over the ship's place in this instance, and is +always the most dangerous part of the storm. As the ship is able to make +good distance from this track by bearing towards the N.W., provided she +has plenty of sea-room, she will experience less of the violence of the +hurricane; but as most of the Atlantic storms sweep over the shore, it +will be desirable to lay-to at some point on the _larboard tack_, the +ship being now in the left-hand semicircle. By moving the circle as +before directed it will be seen that the veering of the wind is now +E.S.E., E., E.N.E., N.E., the lowest barometer N.N.E., N., and N.N.W., +the ship experiencing more or less of these changes as it is nearer to +or farther from the axis line. + +In latitudes lower than 20° N. the Atlantic hurricanes usually move +towards the N.W. Taking the same positions of our ship with regard to +the storms as in the two former examples, if the storm set in with the +wind E. the proper proceeding is to bear away for the N.E., the most +dangerous quadrant of the hurricane having overtaken the ship, the +veering of the wind if she is lying-to will be E., E.S.E., S.E., with +the lowest barometer S.S.E. and S. Should the storm set in at N.E., her +position at the time will be some indication of the distance of the +centre's track from the nearest land, and will greatly assist in +determining the point at which the captain ought to lay-to after taking +advantage of the N.E. wind, should he be able so to do, to bear away +from the centre line, so as to avoid as much as possible the violence of +the storm. From the proximity of the West Indian Islands to this +locality of the storm-paths, the danger is proportionally increased. + +The above examples have reference only to the lower and upper branches +of the storm paths of the Northern Atlantic in the neighbourhood of the +West Indies and the United States. In latitudes from about 25° to 32° +these paths usually _re-curve_, and at some point will move towards the +north. The veering of the wind will consequently be more or less +complicated according as the ship may be nearer to or farther from the +centre. The tables on page 11, combined with the first of those +immediately following the next paragraph, will, it is hoped, prove +advantageous in assisting the mariner as to the course to be adopted. As +a general principle we should say it would be best to bear to the +eastward, so as not only to avoid the greater fury of the storm, but to +get into the S. and S.W. winds, which give the principal chances of +making a westerly course. + +We have in page 44 called attention to the fact that the storm paths +traced by Mr. Redfield do not extend eastward of the 50th meridian. This +by no means precludes the existence of severe storms and those of a +rotatory character in the great basin of the Northern Atlantic, +especially between the 40th and 50th parallels. A remarkable instance +has come under the author's attention of the wind hauling _apparently_ +contrary to the usual theory: it may be that the storm route was in a +direction not generally observed. We are at the present moment destitute +of any information that at all indicates a _reversion_ of the rotation +in either hemisphere. The following tables constructed for the northern +hemisphere, and for storm routes _not yet ascertained_, may probably be +consulted with advantage on anomalous occasions. + + +HURRICANE MOVING FROM SOUTH TO NORTH. + + Axis line, wind E., barometer falling, first half of storm. + Axis line, wind W., barometer rising, last half of storm. + + +RIGHT-HAND SEMICIRCLE. + + Wind E.S.E., S.E., S.S.E., S., barometer falling, first half of storm. + Wind W.S.W., S.W., S.S.W., S., barometer rising, last half of storm. + +LEFT-HAND SEMICIRCLE. + + Wind E.N.E., N.E., N.N.E., N., barometer falling, first half of storm. + Wind W.N.W., N.W., N.N.W., N., barometer rising, last half of storm. + + +HURRICANE MOVING FROM NORTH TO SOUTH. + + Axis line, wind W., barometer falling, first half of storm. + Axis line, wind E., barometer rising, last half of storm. + + +RIGHT-HAND SEMICIRCLE. + + Wind W.N.W., N.W., N.N.W., N., barometer falling, first half of storm. + Wind E.N.E., N.E., N.N.E., N., barometer rising, last half of storm. + + +LEFT-HAND SEMICIRCLE. + + Wind W.S.W., S.W., S.S.W., S., barometer falling, first half of storm. + Wind E.S.E., S.E., S.S.E., S,, barometer rising, last half of storm. + + +HURRICANE MOVING PROM WEST TO EAST. + + Axis line, wind S., barometer falling, first half of storm. + Axis line, wind N., barometer rising, last half of storm. + + +RIGHT-HAND SEMICIRCLE. + + Wind S.S.W., S.W., W.S.W., W., barometer falling, first half of storm. + Wind N.N.W., N.W., W.N.W., W., barometer rising, last half of storm. + + +LEFT-HAND SEMICIRCLE. + + Wind S.S.E., S.E., E.S.E., E., barometer falling, first half of storm. + Wind N.N.E., N.E., E.N.E., E., barometer rising, last half of storm. + +HURRICANE MOVING FROM NORTH-WEST TO SOUTH-EAST. + + Axis line, wind S.W., barometer falling, first half of storm. + Axis line, wind N.E., barometer rising, last half of storm. + + +RIGHT-HAND SEMICIRCLE. + + Wind W.S.W., W., W.N.W., N.W., barometer falling, first half of storm. + Wind N.N.E., N., N.N.W., N.W., barometer rising, last half of storm. + + +LEFT-HAND SEMICIRCLE. + + Wind S.S.W., S., S.S.E., S.E., barometer falling, first half of storm. + Wind E.N.E., E., E.S.E., S.E., barometer rising, last half of storm. + + + + +APPENDIX. + +TABLE I.--Correction to be added to Barometers for Capillary Action. + + +--------------------+---------------------------------+ + | | Correction for | + | Diameter of Tube. |-----------------+---------------| + | | Unboiled Tubes. | Boiled Tubes. | + |--------------------|-----------------|---------------| + | Inch. | Inch. | Inch. | + | 0·60 | 0·004 | 0·002 | + | 0·50 | 0·007 | 0·003 | + | 0·45 | 0·010 | 0·005 | + | 0·40 | 0·014 | 0·007 | + | 0·35 | 0·020 | 0·010 | + | 0·30 | 0·028 | 0·014 | + | 0·25 | 0·040 | 0·020 | + | 0·20 | 0·060 | 0·029 | + | 0·15 | 0·088 | 0·044 | + | 0·10 | 0·142 | 0·070 | + +--------------------+-----------------+---------------+ + + ++---------------------------------------------------------------------+ +|Transcibers note: The following 100 line table has been split into | +|two, both vertically and horizontally, so that it can be accommodated| +|on these pages. | ++---------------------------------------------------------------------+ + + +TABLE II.--Correction to be applied to Barometers with _Brass Scales_, +extending from the Cistern to the top of the Mercurial Column, to reduce +the observation to 32° Fahrenheit. + + + ---+------------------------------------------------------------+---- + | I N C H E S. | + T | -----+-------+------+-------+------+-------+------+--------| T + e | | | | | | | | | e + m | 24 | 24·5 | 25 | 25·5 | 26 | 26·5 | 27 | 27·5 | m + p | | | | | | | | | p + ---+------+-------+------+-------+------+-------+------+--------+---- + ° | + | + | + | + | + | + | + | + | ° + 0 | ·061 | ·063 | ·064 | ·065 | ·067 | ·068 | ·069 | ·071 | 0 + 1 | ·059 | ·061 | ·062 | ·063 | ·064 | ·065 | ·067 | ·068 | 1 + 2 | ·057 | ·058 | ·060 | ·061 | ·062 | ·063 | ·064 | ·066 | 2 + 3 | ·055 | ·056 | ·057 | ·059 | ·060 | ·061 | ·062 | ·063 | 3 + 4 | ·053 | ·054 | ·055 | ·056 | ·057 | ·058 | ·059 | ·061 | 4 + 5 | ·051 | ·052 | ·053 | ·054 | ·055 | ·056 | ·057 | ·058 | 5 + 6 | ·049 | ·050 | ·051 | ·052 | ·053 | ·054 | ·055 | ·056 | 6 + 7 | ·046 | ·047 | ·048 | ·049 | ·050 | ·051 | ·052 | ·053 | 7 + 8 | ·044 | ·045 | ·046 | ·047 | ·048 | ·049 | ·050 | ·051 | 8 + 9 | ·042 | ·043 | ·044 | ·045 | ·046 | ·046 | ·047 | ·048 | 9 + 10 | ·040 | ·041 | ·042 | ·042 | ·043 | ·044 | ·045 | ·046 | 10 + | | | | | | | | | + 11 | ·038 | ·039 | ·039 | ·040 | ·041 | ·042 | ·042 | ·043 | 11 + 12 | ·036 | ·036 | ·037 | ·038 | ·039 | ·039 | ·040 | ·041 | 12 + 13 | ·033 | ·034 | ·035 | ·036 | ·036 | ·037 | ·038 | ·038 | 13 + 14 | ·031 | ·032 | ·033 | ·033 | ·034 | ·035 | ·035 | ·036 | 14 + 15 | ·029 | ·030 | ·030 | ·031 | ·032 | ·032 | ·033 | ·033 | 15 + 16 | ·027 | ·028 | ·028 | ·029 | ·029 | ·030 | ·030 | ·031 | 16 + 17 | ·025 | ·025 | ·026 | ·026 | ·027 | ·027 | ·028 | ·028 | 17 + 18 | ·023 | ·023 | ·024 | ·024 | ·025 | ·025 | ·025 | ·026 | 18 + 19 | ·021 | ·021 | ·021 | ·022 | ·022 | ·023 | ·023 | ·024 | 19 + 20 | ·018 | ·019 | ·019 | ·020 | ·020 | ·020 | ·021 | ·021 | 20 + | | | | | | | | | + 21 | ·016 | ·017 | ·017 | ·017 | ·018 | ·018 | ·018 | ·019 | 21 + 22 | ·014 | ·014 | ·015 | ·015 | ·015 | ·016 | ·016 | ·016 | 22 + 23 | ·012 | ·012 | ·012 | ·013 | ·013 | ·013 | ·013 | ·014 | 23 + 24 | ·010 | ·010 | ·010 | ·010 | ·011 | ·011 | ·011 | ·011 | 24 + 25 | ·008 | ·008 | ·008 | ·008 | ·008 | ·008 | ·009 | ·009 | 25 + 26 | ·005 | ·006 | ·006 | ·006 | ·006 | ·006 | ·006 | ·006 | 26 + 27 | ·003 | ·003 | ·003 | ·003 | ·004 | ·004 | ·004 | ·004 | 27 + 28 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | 28 + | -- | -- | -- | -- | -- | -- | -- | -- | + 29 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | 29 + 30 | ·003 | ·003 | ·003 | ·004 | ·004 | ·004 | ·004 | ·004 | 30 + | | | | | | | | | + 31 | ·005 | ·006 | ·006 | ·006 | ·006 | ·006 | ·006 | ·006 | 31 + 32 | ·008 | ·008 | ·008 | ·008 | ·008 | ·008 | ·008 | ·009 | 32 + 33 | ·010 | ·010 | ·010 | ·010 | ·011 | ·011 | ·011 | ·011 | 33 + 34 | ·012 | ·012 | ·012 | ·013 | ·013 | ·013 | ·013 | ·014 | 34 + 35 | ·014 | ·014 | ·015 | ·015 | ·015 | ·015 | ·016 | ·016 | 35 + 36 | ·016 | ·017 | ·017 | ·017 | ·017 | ·018 | ·018 | ·019 | 36 + 37 | ·018 | ·019 | ·019 | ·019 | ·020 | ·020 | ·021 | ·021 | 37 + 38 | ·020 | ·021 | ·021 | ·022 | ·022 | ·023 | ·023 | ·023 | 38 + 39 | ·023 | ·023 | ·024 | ·024 | ·024 | ·025 | ·025 | ·026 | 39 + 40 | ·025 | ·025 | ·026 | ·026 | ·027 | ·027 | ·028 | ·028 | 40 + | | | | | | | | | + 41 | ·027 | ·027 | ·028 | ·029 | ·029 | ·030 | ·030 | ·031 | 41 + 42 | ·029 | ·030 | ·030 | ·031 | ·031 | ·032 | ·033 | ·033 | 42 + 43 | ·031 | ·032 | ·032 | ·033 | ·034 | ·034 | ·035 | ·036 | 43 + 44 | ·033 | ·034 | ·035 | ·035 | ·036 | ·037 | ·037 | ·038 | 44 + 45 | ·035 | ·036 | ·037 | ·038 | ·038 | ·039 | ·040 | ·041 | 45 + 46 | ·038 | ·038 | ·039 | ·040 | ·041 | ·042 | ·042 | ·043 | 46 + 47 | ·040 | ·041 | ·041 | ·042 | ·043 | ·044 | ·045 | ·046 | 47 + 48 | ·042 | ·043 | ·044 | ·045 | ·045 | ·046 | ·047 | ·048 | 48 + 49 | ·044 | ·045 | ·046 | ·047 | ·043 | ·049 | ·050 | ·050 | 49 + 50 | ·046 | ·047 | ·043 | ·049 | ·050 | ·051 | ·052 | ·053 | 50 + ---+------+-------+------+-------+------+-------+------+--------+---- + + ---+-----------------------------------------------------+---- + | I N C H E S. | + T |-------+------+-------+------+-------+------+--------| T + e | | | | | | | | e + m | 28 | 28·5 | 29 | 29·5 | 30 | 30·5 | 31 | m + p | | | | | | | | p + ---+-------+------+-------+------+-------+------+--------+---- + ° | + | + | + | + | + | + | + | ° + 0 | ·072 | ·073 | ·074 | ·076 | ·077 | ·078 | ·080 | 0 + 1 | ·069 | ·071 | ·072 | ·073 | ·074 | ·076 | ·077 | 1 + 2 | ·067 | ·068 | ·069 | ·070 | ·072 | ·073 | ·074 | 2 + 3 | ·064 | ·065 | ·067 | ·068 | ·069 | ·070 | ·071 | 3 + 4 | ·062 | ·063 | ·064 | ·065 | ·066 | ·067 | ·068 | 4 + 5 | ·039 | ·060 | ·061 | ·062 | ·063 | ·065 | ·066 | 5 + 6 | ·057 | ·058 | ·059 | ·060 | ·061 | ·062 | ·063 | 6 + 7 | ·054 | ·055 | ·056 | ·057 | ·058 | ·059 | ·060 | 7 + 8 | ·052 | ·053 | ·054 | ·054 | ·055 | ·056 | ·057 | 8 + 9 | ·049 | ·050 | ·051 | ·052 | ·053 | ·054 | ·054 | 9 + 10 | ·047 | ·047 | ·048 | ·049 | ·050 | ·051 | ·052 | 10 + | | | | | | | | + 11 | ·044 | ·045 | ·046 | ·046 | ·047 | ·048 | ·049 | 11 + 12 | ·042 | ·042 | ·043 | ·044 | ·045 | ·045 | ·046 | 12 + 13 | ·039 | ·040 | ·040 | ·041 | ·042 | ·043 | ·043 | 13 + 14 | ·037 | ·037 | ·038 | ·038 | ·039 | ·040 | ·040 | 14 + 15 | ·034 | ·035 | ·035 | ·036 | ·036 | ·037 | ·038 | 15 + 16 | ·032 | ·032 | ·033 | ·033 | ·034 | ·034 | ·035 | 16 + 17 | ·029 | ·030 | ·030 | ·031 | ·031 | ·032 | ·032 | 17 + 18 | ·026 | ·027 | ·027 | ·028 | ·028 | ·029 | ·029 | 18 + 19 | ·024 | ·024 | ·025 | ·025 | ·026 | ·026 | ·027 | 19 + 20 | ·021 | ·022 | ·022 | ·023 | ·023 | ·023 | ·024 | 20 + | | | | | | | | + 21 | ·019 | ·019 | ·020 | ·020 | ·020 | ·021 | ·021 | 21 + 22 | ·016 | ·017 | ·017 | ·017 | ·018 | ·018 | ·018 | 22 + 23 | ·014 | ·014 | ·014 | ·015 | ·015 | ·015 | ·015 | 23 + 24 | ·011 | ·012 | ·012 | ·012 | ·012 | ·012 | ·013 | 24 + 25 | ·009 | ·009 | ·009 | ·009 | ·009 | ·010 | ·010 | 25 + 26 | ·006 | ·006 | ·007 | ·007 | ·007 | ·007 | ·007 | 26 + 27 | ·004 | ·004 | ·004 | ·004 | ·004 | ·004 | ·004 | 27 + 28 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | 28 + | -- | -- | -- | -- | -- | -- | -- | + 29 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | ·001 | 29 + 30 | ·004 | ·004 | ·004 | ·004 | ·004 | ·004 | ·004 | 30 + | | | | | | | | + 31 | ·006 | ·006 | ·007 | ·007 | ·007 | ·007 | ·007 | 31 + 32 | ·009 | ·009 | ·009 | ·009 | ·009 | ·010 | ·010 | 32 + 33 | ·011 | ·012 | ·012 | ·012 | ·012 | ·012 | ·012 | 33 + 34 | ·014 | ·014 | ·014 | ·015 | ·015 | ·015 | ·015 | 34 + 35 | ·016 | ·017 | ·017 | ·017 | ·018 | ·018 | ·018 | 35 + 36 | ·019 | ·019 | ·020 | ·020 | ·020 | ·021 | ·021 | 36 + 37 | ·021 | ·022 | ·022 | ·022 | ·023 | ·023 | ·024 | 37 + 38 | ·024 | ·024 | ·025 | ·025 | ·026 | ·026 | ·026 | 38 + 39 | ·026 | ·027 | ·027 | ·028 | ·028 | ·029 | ·029 | 39 + 40 | ·029 | ·029 | ·030 | ·030 | ·031 | ·031 | ·032 | 40 + | | | | | | | | + 41 | ·031 | ·032 | ·033 | ·033 | ·034 | ·034 | ·035 | 41 + 42 | ·034 | ·034 | ·035 | ·036 | ·036 | ·037 | ·037 | 42 + 43 | ·036 | ·037 | ·038 | ·038 | ·039 | ·010 | ·040 | 43 + 44 | ·039 | ·040 | ·040 | ·041 | ·042 | ·042 | ·043 | 44 + 45 | ·041 | ·042 | ·043 | ·044 | ·044 | ·045 | ·046 | 45 + 46 | ·044 | ·045 | ·045 | ·046 | ·047 | ·048 | ·049 | 46 + 47 | ·046 | ·047 | ·048 | ·049 | ·050 | ·051 | ·051 | 47 + 48 | ·049 | ·050 | ·051 | ·052 | ·052 | ·053 | ·054 | 48 + 49 | ·031 | ·052 | ·053 | ·054 | ·055 | ·056 | ·057 | 49 + 50 | ·054 | ·055 | ·056 | ·057 | ·058 | ·059 | ·060 | 50 + ---+-------+------+-------+------+-------+------+--------+---- + + +TABLE II.--_Continued_ + + ----+------------------------------------------------------------+----- + | I N C H E S. | + T |------+-------+------+-------+------+-------+------+--------| T + e | | | | | | | | | e + m | 24 | 24·5 | 25 | 25·5 | 26 | 26·5 | 27 | 27·5 | m + p | | | | | | | | | p + ----+------+-------+------+-------+------+-------+------+--------+----- + ° | + | + | + | + | + | + | + | + | ° + 51 | ·048 | ·049 | ·050 | ·051 | ·052 | ·053 | ·054 | ·055 | 51 + 52 | ·050 | ·052 | ·053 | ·054 | ·055 | ·056 | ·057 | ·058 | 52 + 53 | ·053 | ·054 | ·055 | ·056 | ·057 | ·058 | ·059 | ·060 | 53 + 54 | ·055 | ·056 | ·057 | ·053 | ·059 | ·060 | ·062 | ·063 | 54 + 55 | ·057 | ·058 | ·059 | ·060 | ·062 | ·063 | ·064 | ·065 | 55 + 56 | ·059 | ·060 | ·061 | ·063 | ·064 | ·065 | ·066 | ·063 | 56 + 57 | ·061 | ·062 | ·064 | ·065 | ·066 | ·068 | ·069 | ·070 | 57 + 58 | ·063 | ·065 | ·066 | ·067 | ·069 | ·070 | ·071 | ·073 | 58 + 59 | ·065 | ·067 | ·068 | ·070 | ·071 | ·072 | ·074 | ·075 | 59 + 60 | ·068 | ·069 | ·070 | ·072 | ·073 | ·075 | ·076 | ·077 | 60 + | | | | | | | | | + 61 | ·070 | ·071 | ·073 | ·074 | ·075 | ·077 | ·078 | ·080 | 61 + 62 | ·072 | ·073 | ·075 | ·076 | ·078 | ·079 | ·081 | ·082 | 62 + 63 | ·074 | ·076 | ·077 | ·079 | ·080 | ·082 | ·083 | ·085 | 63 + 64 | ·076 | ·073 | ·079 | ·081 | ·082 | ·084 | ·086 | ·087 | 64 + 65 | ·078 | ·080 | ·082 | ·083 | ·085 | ·086 | ·088 | ·090 | 65 + 66 | ·080 | ·082 | ·084 | ·085 | ·087 | ·089 | ·090 | ·092 | 66 + 67 | ·083 | ·084 | ·086 | ·088 | ·089 | ·091 | ·093 | ·095 | 67 + 68 | ·085 | ·086 | ·088 | ·090 | ·092 | ·094 | ·095 | ·097 | 68 + 69 | ·087 | ·089 | ·090 | ·092 | ·094 | ·096 | ·098 | ·100 | 69 + 70 | ·089 | ·091 | ·093 | ·095 | ·096 | ·098 | ·100 | ·102 | 70 + | | | | | | | | | + 71 | ·091 | ·093 | ·095 | ·097 | ·099 | ·101 | ·102 | ·104 | 71 + 72 | ·093 | ·095 | ·097 | ·099 | ·101 | ·103 | ·105 | ·107 | 72 + 73 | ·095 | ·097 | ·099 | ·101 | ·103 | ·105 | ·107 | ·109 | 73 + 74 | ·097 | ·099 | ·102 | ·104 | ·106 | ·108 | ·110 | ·112 | 74 + 75 | ·100 | ·102 | ·104 | ·106 | ·108 | ·110 | ·112 | ·114 | 75 + 76 | ·102 | ·104 | ·106 | ·108 | ·110 | ·112 | ·114 | ·117 | 76 + 77 | ·104 | ·106 | ·108 | ·110 | ·112 | ·115 | ·117 | ·119 | 77 + 78 | ·106 | ·108 | ·110 | ·113 | ·115 | ·117 | ·119 | ·122 | 78 + 79 | ·108 | ·110 | ·113 | ·115 | ·117 | ·119 | ·122 | ·124 | 79 + 80 | ·110 | ·113 | ·115 | ·117 | ·119 | ·122 | ·124 | ·126 | 80 + | | | | | | | | | + 81 | ·112 | ·115 | ·117 | ·119 | ·122 | ·124 | ·126 | ·129 | 81 + 82 | ·114 | ·117 | ·119 | ·122 | ·124 | ·126 | ·129 | ·131 | 82 + 83 | ·117 | ·119 | ·121 | ·124 | ·126 | ·129 | ·131 | ·134 | 83 + 84 | ·119 | ·121 | ·124 | ·126 | ·129 | ·131 | ·134 | ·136 | 84 + 85 | ·121 | ·123 | ·136 | ·128 | ·131 | ·133 | ·136 | ·139 | 85 + 86 | ·123 | ·126 | ·128 | ·131 | ·133 | ·136 | ·138 | ·141 | 86 + 87 | ·125 | ·128 | ·130 | ·133 | ·136 | ·138 | ·141 | ·143 | 87 + 88 | ·127 | ·130 | ·133 | ·133 | ·138 | ·141 | ·143 | ·146 | 88 + 89 | ·129 | ·132 | ·135 | ·137 | ·140 | ·143 | ·146 | ·148 | 89 + 90 | ·131 | ·134 | ·137 | ·140 | ·142 | ·145 | ·148 | ·151 | 90 + | | | | | | | | | + 91 | ·134 | ·136 | ·139 | ·142 | ·145 | ·148 | ·150 | ·153 | 91 + 92 | ·136 | ·139 | ·141 | ·144 | ·147 | ·150 | ·153 | ·156 | 92 + 93 | ·138 | ·141 | ·144 | ·147 | ·149 | ·152 | ·155 | ·158 | 93 + 94 | ·140 | ·143 | ·146 | ·149 | ·152 | ·155 | ·157 | ·161 | 94 + 95 | ·142 | ·145 | ·148 | ·151 | ·154 | ·157 | ·160 | ·163 | 95 + 96 | ·144 | ·147 | ·150 | ·153 | ·156 | ·159 | ·162 | ·165 | 96 + 97 | ·146 | ·149 | ·152 | ·155 | ·159 | ·162 | ·165 | ·168 | 97 + 98 | ·148 | ·152 | ·155 | ·158 | ·161 | ·164 | ·167 | ·170 | 98 + 99 | ·151 | ·154 | ·157 | ·160 | ·163 | ·166 | ·169 | ·173 | 99 + 100 | ·153 | ·156 | ·159 | ·162 | ·165 | ·169 | ·172 | ·175 | 100 + ----+------+-------+------+-------+------+-------+------+--------+----- + + + ----+-----------------------------------------------------+----- + | I N C H E S. | + T |-------+------+-------+------+-------+------+--------| T + e | | | | | | | | e + m | 28 | 28·5 | 29 | 29·5 | 30 | 30·5 | 31 | m + p | | | | | | | | p + ----+-------+------+-------+------+-------+------+--------+----- + ° | + | + | + | + | + | + | + | ° + 51 | ·056 | ·057 | ·058 | ·059 | ·060 | ·061 | ·062 | 51 + 52 | ·059 | ·060 | ·061 | ·062 | ·063 | ·064 | ·065 | 52 + 53 | ·061 | ·063 | ·064 | ·065 | ·066 | ·067 | ·068 | 53 + 54 | ·064 | ·065 | ·066 | ·067 | ·068 | ·070 | ·071 | 54 + 55 | ·066 | ·068 | ·069 | ·070 | ·071 | ·072 | ·073 | 55 + 56 | ·069 | ·070 | ·071 | ·073 | ·074 | ·075 | ·076 | 56 + 57 | ·071 | ·073 | ·074 | ·075 | ·076 | ·078 | ·079 | 57 + 58 | ·074 | ·075 | ·077 | ·078 | ·079 | ·081 | ·082 | 58 + 59 | ·076 | ·078 | ·079 | ·080 | ·082 | ·083 | ·085 | 59 + 60 | ·079 | ·080 | ·082 | ·083 | ·085 | ·086 | ·087 | 60 + | | | | | | | | + 61 | ·081 | ·083 | ·084 | ·086 | ·087 | ·089 | ·090 | 61 + 62 | ·084 | ·085 | ·087 | ·088 | ·090 | ·091 | ·093 | 62 + 63 | ·086 | ·088 | ·089 | ·091 | ·093 | ·094 | ·096 | 63 + 64 | ·089 | ·090 | ·092 | ·094 | ·095 | ·097 | ·098 | 64 + 65 | ·091 | ·093 | ·095 | ·096 | ·098 | ·100 | ·101 | 65 + 66 | ·094 | ·096 | ·097 | ·099 | ·101 | ·102 | ·104 | 66 + 67 | ·096 | ·098 | ·100 | ·102 | ·103 | ·105 | ·107 | 67 + 68 | ·099 | ·101 | ·102 | ·104 | ·106 | ·108 | ·109 | 68 + 69 | ·101 | ·103 | ·105 | ·107 | ·109 | ·110 | ·112 | 69 + 70 | ·104 | ·106 | ·108 | ·109 | ·111 | ·113 | ·115 | 70 + | | | | | | | | + 71 | ·106 | ·108 | ·110 | ·112 | ·114 | ·116 | ·118 | 71 + 72 | ·109 | ·111 | ·113 | ·115 | ·117 | ·119 | ·120 | 72 + 73 | ·111 | ·113 | ·115 | ·117 | ·119 | ·121 | ·123 | 73 + 74 | ·114 | ·116 | ·118 | ·120 | ·122 | ·124 | ·126 | 74 + 75 | ·116 | ·118 | ·120 | ·122 | ·125 | ·127 | ·129 | 75 + 76 | ·119 | ·121 | ·123 | ·125 | ·127 | ·129 | ·131 | 76 + 77 | ·121 | ·123 | ·126 | ·128 | ·130 | ·132 | ·134 | 77 + 78 | ·124 | ·126 | ·128 | ·130 | ·133 | ·135 | ·137 | 78 + 79 | ·126 | ·128 | ·131 | ·133 | ·135 | ·137 | ·140 | 79 + 80 | ·129 | ·131 | ·133 | ·136 | ·138 | ·140 | ·143 | 80 + | | | | | | | | + 81 | ·131 | ·134 | ·136 | ·138 | ·141 | ·143 | ·145 | 81 + 82 | ·134 | ·136 | ·138 | ·141 | ·143 | ·146 | ·148 | 82 + 83 | ·136 | ·139 | ·141 | ·143 | ·146 | ·148 | ·151 | 83 + 84 | ·139 | ·141 | ·144 | ·146 | ·149 | ·151 | ·154 | 84 + 85 | ·141 | ·144 | ·146 | ·149 | ·151 | ·154 | ·156 | 85 + 86 | ·144 | ·146 | ·149 | ·151 | ·154 | ·156 | ·159 | 86 + 87 | ·146 | ·149 | ·151 | ·154 | ·157 | ·159 | ·162 | 87 + 88 | ·149 | ·151 | ·154 | ·157 | ·159 | ·162 | ·165 | 88 + 89 | ·151 | ·154 | ·156 | ·159 | ·162 | ·165 | ·167 | 89 + 90 | ·153 | ·156 | ·159 | ·162 | ·164 | ·167 | ·170 | 90 + | | | | | | | | + 91 | ·156 | ·159 | ·162 | ·165 | ·167 | ·170 | ·173 | 91 + 92 | ·158 | ·161 | ·164 | ·167 | ·170 | ·172 | ·175 | 92 + 93 | ·161 | ·164 | ·167 | ·170 | ·172 | ·175 | ·178 | 93 + 94 | ·163 | ·166 | ·169 | ·172 | ·175 | ·177 | ·180 | 94 + 95 | ·166 | ·169 | ·172 | ·175 | ·178 | ·180 | ·183 | 95 + 96 | ·168 | ·171 | ·174 | ·178 | ·181 | ·183 | ·116 | 96 + 97 | ·171 | ·174 | ·177 | ·180 | ·183 | ·186 | ·189 | 97 + 98 | ·173 | ·176 | ·179 | ·183 | ·186 | ·188 | ·191 | 98 + 99 | ·176 | ·179 | ·182 | ·185 | ·188 | ·191 | ·194 | 99 + 100 | ·178 | ·181 | ·184 | ·188 | ·191 | ·194 | ·197 | 100 + ----+-------+------+-------+------+-------+------+--------+----- + + +PRINTED BY W. CLOWES AND SONS, STANFORD STREET. FOOTNOTES: + +[1] The first half of the storm, _in the case before alluded to_, is +that N.E. of the line N.W.--S.E., fig. 1, comprising the easterly and +southerly winds; and the latter half, that S.W. of the same line, +comprising the northerly and westerly winds. + +[2] This table is also applicable to the hurricanes in the neighbourhood +of Mauritius in the southern hemisphere, where all the phænomena are +reversed; the motion of the hurricanes being towards the S.W., and the +rotation in the direction of the hands of a watch, the same barometric +and anemonal phænomena are experienced as in a hurricane in the northern +hemisphere moving towards the N.E. + +[3] By the officer of the watch being charged with this duty, and its +being executed under his immediate superintendence, it is apprehended +that a register may be kept with great regularity. + +[4] These papers may be obtained from Messrs. W. H. Allen and Co., +Booksellers to the Honourable East India Company, No. 7, Leadenhall +Street, London. + +[5] Reports of the British Association for the Advancement of Science, +1846, p. 139. + + + + + + +End of Project Gutenberg's The Hurricane Guide, by William Radcliff Birt + +*** END OF THIS PROJECT GUTENBERG EBOOK THE HURRICANE GUIDE *** + +***** This file should be named 18534-8.txt or 18534-8.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/1/8/5/3/18534/ + +Produced by Carlos Traversi, Janet Blenkinship, and the +Online Distributed Proofreaders Europe at +http://dp.rastko.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Hurricane Guide + Being An Attempt To Connect The Rotary Gale Or Revolving + Storm With Atmospheric Waves. + +Author: William Radcliff Birt + +Release Date: June 8, 2006 [EBook #18534] + +Language: English + +Character set encoding: ISO-8859-1 + +*** START OF THIS PROJECT GUTENBERG EBOOK THE HURRICANE GUIDE *** + + + + +Produced by Carlos Traversi, Janet Blenkinship, and the +Online Distributed Proofreaders Europe at +http://dp.rastko.net + + + + + + +</pre> + +<p><span class='pagenum'><a name="Page_1" id="Page_1">[Pg 1]</a></span></p> + + + + +<h1>THE</h1> + +<h1>HURRICANE GUIDE:</h1> + +<h4>BEING</h4> + +<h3>AN ATTEMPT TO CONNECT THE</h3> + +<h2>ROTATORY GALE OR REVOLVING STORM</h2> + +<h4>WITH</h4> + +<h2>ATMOSPHERIC WAVES.</h2> + +<h4>INCLUDING INSTRUCTIONS FOR OBSERVING THE PHÆNOMENA OF THE WAVES AND +STORMS;</h4> + +<h5>WITH</h5> + +<h4>PRACTICAL DIRECTIONS FOR AVOIDING THE CENTRES OF THE LATTER.</h4> + +<h3>BY</h3> + +<h2>WILLIAM RADCLIFF BIRT.</h2> + + +<p class='center'>LONDON: JOHN MURRAY, ALBEMARLE STREET.<br /> +<i>PUBLISHER TO THE ADMIRALTY.</i><br /> +1850.<span class='pagenum'><a name="Page_2" id="Page_2">[Pg 2]</a></span><br /> +PRINTED BY W. CLOWES AND SONS, STAMFORD STREET.<span class='pagenum'><a name="Page_3" id="Page_3">[Pg 3]</a></span></p> + + + +<hr style="width: 65%;" /> +<h2>PREFACE.</h2> + + +<p>In introducing the following pages to the notice of the Public, it is +the Author's wish to exhibit in as clear a light as our present +researches on the subjects treated of will allow, the connexion between +one of the most terrific phænomena with which our globe is visited, and +a phænomenon which, although but little known, appears to be intimately +connected with revolving storms. How far he has succeeded, either in +this particular object or in endeavouring to render the essential +phænomena of storms familiar to the seaman, is left for the Public to +determine. Should any advantage be found to result from the study of the +Atmospheric Waves, as explained and recommended in this little work, or +the seaman be induced by its perusal to attend more closely to the +observations of those instruments that are calculated to warn him of his +danger, an object will be attained strikingly illustrative of the +Baconian aphorism, "Knowledge is Power."</p> + +<p><span style="margin-left: 2em;"><i>Bethnal Green</i>, April 19, 1849.</span><span class='pagenum'><a name="Page_5" id="Page_5">[Pg 5]</a></span><span class='pagenum'><a name="Page_4" id="Page_4">[Pg 4]</a></span></p> + + + +<hr style="width: 65%;" /> +<h2>CONTENTS.</h2> + +<div class='center'> +<table border="0" cellpadding="4" cellspacing="0" summary="Contents"> +<tr><td align='left'>CHAP.</td><td align='left'>I.--<span class="smcap">Phænomena of Revolving Storms</span></td><td align='right'><a href='#Page_7'>7</a></td></tr> +<tr><td align='center'>"</td><td align='left'>II.--<span class="smcap">Phænomena of Atmospheric Waves</span></td><td align='right'><a href='#Page_13'>13</a></td></tr> +<tr><td align='center'>"</td><td align='left'>III.--<span class="smcap">Observations</span></td><td align='right'><a href='#Page_18'>18</a></td></tr> +<tr><td align='left'> </td><td align='left'><span style="margin-left: 2em;">SECT.I.--Instruments</span></td><td align='right'><a href='#Page_19'>19</a></td></tr> +<tr><td align='left'> </td><td align='left'><span style="margin-left: 2em;">SECT. II.--Times of Observation</span></td><td align='right'><a href='#Page_28'>28</a></td></tr> +<tr><td align='left'> </td><td align='left'><span style="margin-left: 2em;">SECT. III.--Localities for Additional Observations</span></td><td align='right'><a href='#Page_31'>31</a></td></tr> +<tr><td align='left'> </td><td align='left'><span style="margin-left: 2em;">SECT. IV.--Storms, Hurricanes, and Typhoons</span></td><td align='right'><a href='#Page_43'>43</a></td></tr> +<tr><td align='left'> </td><td align='left'><span style="margin-left: 2em;">SECT. V.--Seasons for Extra Observations</span></td><td align='right'><a href='#Page_48'>48</a></td></tr> +<tr><td align='center'>"</td><td align='left'>IV.--<span class="smcap">Practical Directions for Avoiding the Centres of Storms</span></td><td align='right'><a href='#Page_52'>52</a></td></tr> +</table></div> + + +<p><span class='pagenum'><a name="Page_6" id="Page_6">[Pg 6]</a></span></p> + + + +<hr style="width: 65%;" /> +<h2>NOTICE.</h2> + + +<p>In the pocket accompanying this work are two rings of stiff cardboard, +on which will be found all the information contained in figures 1 and 2. +When they are laid flatly upon a chart, the continuity of the lines on +the chart is not materially interfered with, while the idea of a body of +air rotating in the direction indicated by the arrows is conspicuously +presented to the mind. These rings are more particularly referred to on +<a href='#Page_52'><b>page 52</b></a>.<span class='pagenum'><a name="Page_7" id="Page_7">[Pg 7]</a></span></p> + + + +<hr style="width: 65%;" /> +<h1>THE</h1> + +<h1>HURRICANE GUIDE.</h1> + + + + +<hr style="width: 65%;" /> +<h2>CHAPTER I.</h2> + +<h3>PHÆNOMENA OF REVOLVING STORMS.</h3> + + +<p>It is the object of the following pages to exhibit, so far as +observation may enable us, and in as brief a manner as possible, the +connexion, if any, that exists between those terrific meteorological +phænomena known as "revolving storms," and those more extensive and +occult but not less important phænomena, "atmospheric waves."</p> + +<p>To the great body of our seamen, whether in her Majesty's or the +mercantile service, the subject can present none other than the most +interesting features. The laws that govern the transmission of large +bodies of air from one part of the oceanic surface to another, either in +a state of rapid rotation or presenting a more or less rectilineal +direction, must at all times form an important matter of inquiry, and +bear very materially on the successful prosecution of the occupation of +the voyager.</p> + +<p>In order to place the subjects above alluded to in such a point of view +that the connexion between them may be readily seen, it will be +important to notice the principal<span class='pagenum'><a name="Page_8" id="Page_8">[Pg 8]</a></span> phænomena presented by each. Without +going over the ground so well occupied by those able writers on the +subject of storms—Redfield, Reid, Piddington, and Thom—it will be +quite sufficient for our present purpose simply to notice the essential +phænomena of revolving storms as manifested by the barometer and vane. +The usual indications of a storm in connexion with these instruments are +the <i>falling</i> of the barometer and the <i>freshening</i> of the wind, and it +is generally considered that a <i>rapid</i> fall of the mercury in the +hurricane regions invariably precedes the setting in of a storm.</p> + +<p>There are three classes of phænomena that present themselves to an +observer, according as he is situated <i>on</i> the line or axis of +translation, or <i>in</i> either the right or left hand semicircle of the +storm. These will be rendered very apparent by a little attention to the +annexed engraving, fig. 1.</p> + +<div class="figcenter"><img src="images/img008.jpg" alt="Fig. 1" title="Fig. 1" /></div> +<p><span class='pagenum'><a name="Page_9" id="Page_9">[Pg 9]</a></span></p> + +<p>In this figure the arrow-head is supposed to be directed true north, and +the hurricane—as is the case in the American storms north of the 30th +parallel—to be moving towards the N.E. on the line N.E.—S.W. If the +ship take the hurricane with the wind S.E.,—the letters within the two +larger circles indicating <i>the direction of the wind in the storm</i> +according to the rotation as shown by the circle of arrow-heads, and +which it is to be particularly noted is in the northern hemisphere +<i>contrary to the direction in which the hands of a watch move</i>: in the +southern hemisphere the rotation is reversed—the only phænomena +presented by the storm are as follows:—The wind continues to blow from +the S.E., increasing considerably in force with the barometer falling to +a very great extent until the centre of the storm reaches the ship, when +the fury of the winds is hushed, and a lull or calm takes place, +generally for about half an hour, after which the wind springs up mostly +with increased violence, but from the opposite quarter N.W., the +barometer begins to rise, and as the storm passes off, the force of the +wind abates.</p> + +<p>The point to which we wish particularly to direct attention in connexion +with this exposition of the phænomena attending the transmission of a +storm is this:—If the observer so place himself at the commencement +that the wind passes <i>from his left hand towards his right</i>, his face +will be directed towards the centre of the storm; and the wind +undergoing no change in direction, but only in force, will acquaint him +with this important fact that the <i>centre</i> is not only gradually but +surely approaching him: in other words, in the case before us, when he +finds the wind from the S.E., and he places himself with his face to the +S.W. he is looking towards the centre, and the wind<span class='pagenum'><a name="Page_10" id="Page_10">[Pg 10]</a></span> rushes past him +<i>from his left to his right hand</i>. Now the connexion of the barometer +with this phase of the storm is <i>falling with the wind from left to +right, the observer facing the centre while the first half is +transiting</i>.<a name="FNanchor_1_1" id="FNanchor_1_1"></a><a href="#Footnote_1_1" class="fnanchor">[1]</a> During the latter half these conditions are reversed, +the observer still keeping his position, his face directed to the S.W., +the barometer <i>rises</i> with a N.W. wind, which rushes past him <i>from his +right to his left hand</i> with a decreasing force. We have therefore <i>a +rising barometer with the wind from right to left during the latter half +of the storm, the observer having his back to the centre</i>.</p> + +<p>The above <i>general</i> enunciations of the barometric and anemonal +phænomena of a rotating storm hold good with regard to the <i>northern</i> +hemisphere, whatever may be the direction in which the hurricanes +advance. This may be placed in a clearer light, as well as the remaining +classes of phænomena shown, by consulting the following tables, +constructed for the basin of the Northern Atlantic, and comparing them +with fig. 1. In this basin, with lower latitudes than 25°, the usual +paths of the hurricanes are towards the north-west, in higher latitudes +than 30° towards the north-east. The tables exhibit the veering of the +wind with the movements of the barometer, according as the ship is +situated in the right or left hand semicircle of the hurricane. It must +here be understood that the right and left hand semicircles are +determined by the observer so placing himself that his face is directed +towards the quarter to which the hurricane is advancing.<span class='pagenum'><a name="Page_11" id="Page_11">[Pg 11]</a></span></p> + +<h4>LOWER LATITUDES.</h4> + +<p class='center'>NORTHERN HEMISPHERE.</p> + +<p> +<span style="margin-left: 1em;">Axis line, wind N.E., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Axis line, wind S.W., barometer rising, last half of storm.</span><br /> +</p> + +<p class='center'>RIGHT-HAND SEMICIRCLE.</p> + +<p> +<span style="margin-left: 1em;">Wind E.N.E., E., E.S.E., S.E., barometer falling, storm increasing.</span><br /> +<span style="margin-left: 1em;">Wind S.S.W., S., S.S.E., S.E., barometer rising, storm passing off.</span><br /> +</p> + +<p class='center'>LEFT-HAND SEMICIRCLE.</p> + +<p> +<span style="margin-left: 1em;">Wind N.N.E., N., N.N.W., N.W., barometer falling, storm increasing.</span><br /> +<span style="margin-left: 1em;">Wind W.S.W., W., W.N.W., N.W., barometer rising, storm passing off.</span><br /> +</p> + + +<h4>HIGHER LATITUDES.</h4> + +<p class='center'>NORTHERN HEMISPHERE.<a name="FNanchor_2_2" id="FNanchor_2_2"></a><a href="#Footnote_2_2" class="fnanchor">[2]</a></p> + +<p> +<span style="margin-left: 1em;">Axis line, wind S.E., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Axis line, wind N.W., barometer rising, last half of storm.</span><br /> +</p> + +<h4>RIGHT-HAND SEMICIRCLE.</h4> + +<p> +<span style="margin-left: 1em;">Wind S.S.E., S., S.S.W., S.W., barometer falling, storm increasing.</span><br /> +<span style="margin-left: 1em;">Wind W.N.W., W., W.S.W., S.W., barometer rising, storm passing off.</span><br /> +</p> + +<h4>LEFT-HAND SEMICIRCLE.</h4> + +<p> +<span style="margin-left: 1em;">Wind E.S.E., E., E.N.E., N.E., barometer falling, storm increasing.</span><br /> +<span style="margin-left: 1em;">Wind N.N.W., N., N.N.E., N.E., barometer rising, storm passing off.</span><br /> +</p> + +<p>N.B. The directions of the hurricane winds are so arranged as to show +the points of commencement and termination. Thus in the lower latitudes +a storm commencing at E.N.E. passes off at S.S.W. after the wind<span class='pagenum'><a name="Page_12" id="Page_12">[Pg 12]</a></span> has +veered E., E.S.E., S.E., S.S.E., and S., being in the order of the +letters in the upper line and contrary to their order in the lower. One +commencing at E.S.E. passes off at S.S.E. right-hand semicircle. In the +higher latitudes a ship taking the storm at E.N.E. will be in the +left-hand semicircle, and the hurricane will pass off at N.N.E. These +changes are rendered very apparent by moving the hurricane circle in the +direction in which the storm is expected to proceed.</p> + +<p>Fig. 2 represents the whirl and hurricane winds in the south.</p> +<div class="figcenter"><img src="images/img012.jpg" alt="Fig. 2" title="Fig. 2" /></div> +<p><span class='pagenum'><a name="Page_13" id="Page_13">[Pg 13]</a></span></p> + + + +<hr style="width: 65%;" /> +<h2>CHAPTER II.</h2> + +<h3>PHÆNOMENA OF ATMOSPHERIC WAVES.</h3> + + +<p>Professor Dove of Berlin has suggested that in the temperate zones the +compensating currents of the atmosphere necessary to preserve its +equilibrium may be arranged as parallel currents on the <i>surface</i>, and +not superposed as in or near the torrid zone. His views may be thus +enunciated:—That in the parallels of central Europe the N.E. current +flowing towards the equator to feed the ascending column of heated air +is not compensated by a current in the upper regions of the atmosphere +flowing from the S.W. as in the border of the torrid zone, but there are +also S.W. currents on each side the N.E., which to the various countries +over which they pass appear as surface-winds, the winds in fact being +disposed in alternate beds or layers, S.W., N.E., as in fig. 3.</p> + +<p><span class='pagenum'><a name="Page_14" id="Page_14">[Pg 14]</a></span></p> + +<div class="figcenter"><img src="images/img013.jpg" alt="Fig. 3" title="Fig. 3" /></div> +<p>The Professor also suggests that these parallel and oppositely directed +winds are shifting, <i>i. e.</i> they gradually change their position with a +lateral motion in the direction of the large arrow cutting them +transversely.</p> + +<p>In the course of the author's researches on atmospheric waves he had an +opportunity of testing the correctness of Professor Dove's suggestion, +and in addition ascertained that there existed another set of oppositely +directed winds at right angles to those supposed to exist by the +Professor. These currents were N.W. and S.E. with a lateral motion +towards the N.E. He also carefully discussed the barometric phænomena +with relation to both these sets of currents, and arrived at the +following conclusions. The details will be found in the author's third +report, presented to the British Association for the Advancement of +Science (Reports, 1846, pp. 132 to 162). During the period under +examination the author found the barometer generally to rise with N.E. +and N.W. winds, and fall with S.W. and S.E. winds, and that the +phænomena might be thus illustrated:—Let the strata <i>a a a' a', b' b' b +b</i>, fig. 3, represent two parallel aërial currents or winds, <i>a a a' a'</i> +from S.W. or S.E., and <i>b' b' b b</i> from N.E. or N.W. and conceive them +both to advance from the N.W. in the first instance and from the S.W. in +the second, in the direction of the large arrow. Now conceive the +barometer to commence rising just as the edge <i>b b</i> passes any line of +country, and to continue rising until the edge <i>b' b'</i> arrives at that +line, when the maximum is attained. It will be remarked that this rise +is coincident with a N.E. or N.W. wind. The wind now changes and the +barometer begins to fall, and continues falling until the edge <i>a a</i> +coincides<span class='pagenum'><a name="Page_15" id="Page_15">[Pg 15]</a></span> with the line of country on which <i>b b</i> first impinged. +During this process we have all the phænomena exhibited by an +atmospheric wave: when the edge <i>b b</i> passes a line of country the +barometer is at a <i>minimum</i>, and this minimum has been termed the +<i>anterior trough</i>. During the period the stratum <i>b' b' b b</i> transits, +the barometer rises, and this rise has been called the <i>anterior slope</i>. +When the conterminous edges of the strata <i>a' a' b' b'</i> pass, a +barometric <i>maximum</i> extends along the line of country formerly occupied +by the anterior trough, and this maximum has been designated the +<i>crest</i>. During the transit of the stratum <i>a' a' a a</i> the barometer +<i>falls</i>, and this fall has been characterised as the <i>posterior slope</i>; +and when the edge <i>a a</i> occupies the place of <i>b b</i>, the descent of the +mercurial column is completed, another <i>minimum</i> extends in the +direction of the former, and this minimum has been termed the <i>posterior +trough</i>.</p> + +<p>It will be readily seen that the lateral passage of the N.W. and S.E. +currents towards the N.E. presents precisely the same barometric and +anemonal phænomena as the rotatory storms when moving in the same +direction. If the observer, when the barometer is at a <i>maximum</i> with a +N.W. wind, place himself in the same position with regard to the +laterally advancing current as he did with regard to the advancing +storm, <i>i. e.</i> with his face <i>towards</i> the quarter from which it is +advancing—S.W., he will find that with a <i>falling barometer and S.E. +wind the current passes him from the left to the right hand</i>; but if at +a barometric <i>minimum</i> he place himself in the same position with his +face directed to the quarter from which the N.W. current is advancing +laterally, also S.W., he<span class='pagenum'><a name="Page_16" id="Page_16">[Pg 16]</a></span> will find that with a rising barometer <i>and +N.W. wind the current passes him from right to left</i>. Now the two +classes of phænomena are identical, and it would not be difficult to +show that, had we an instance of a rotatory storm in the northern +hemisphere moving from N.W. to S.E., it would present precisely the same +phænomena as to the direction of currents passing from left to right and +from right to left with falling and rising barometers, increase and +decrease in the force of the wind, &c., as the oppositely directed +aërial currents do which pass over western central Europe.</p> + +<p>In the absence of direct evidence of the production of a revolving storm +from the crossing of two large waves, as suggested by Sir John Herschel, +although it is not difficult to obtain such evidence, especially from +the surface of the ocean, the identity of the two classes of phænomena +exhibited by the storms and waves as above explained amounts to a strong +presumption that there is a close connexion between them, and that a +more minute investigation of the phænomena of atmospheric waves is +greatly calculated to throw considerable light on the laws that govern +the storm paths in both hemispheres. The localities in which these +atmospheric movements, the waves, have been hitherto studied, have been +confined to the northern and central parts of Europe—the west of +Ireland, Alten in the north of Europe, Lougan near the Sea of Azov, and +Geneva, being the angular points of the included area. It will be +remarked that the greatest portion of this area is <i>inland</i>, but there +is one important feature which the study of the barometer has brought to +light, and which is by no means devoid of significance, viz. that<span class='pagenum'><a name="Page_17" id="Page_17">[Pg 17]</a></span> the +oscillations are much greater in the neighbourhood of <i>water</i>, and this +appears to indicate that the junction lines of land and water form by +far the most important portions of the globe in which to study both the +phænomena of storms and waves. It is also very desirable that our +knowledge of these phænomena should, with immediate reference to the +surface of the ocean, be increased, and in this respect captains and +masters of vessels may render essential service by observing and +recording the state of the barometer, and direction and force of the +wind, several times in the course of the day and night;<a name="FNanchor_3_3" id="FNanchor_3_3"></a><a href="#Footnote_3_3" class="fnanchor">[3]</a> and when it +is considered that the immediate object in view is one in which the +mariner is personally interested, and one in which, it may be, his own +safety is concerned, it is hoped that the keeping of a meteorological +register having especial reference to the indications of the barometer, +and force and direction of the wind, will not be felt as irksome, but +rather will be found an interesting occupation, the instruments standing +in the place of faithful monitors, directing when and where to avoid +danger, and the record furnishing important data whereby the knowledge +of general laws may be arrived at, having an essential bearing on the +interests of the service at large.<span class='pagenum'><a name="Page_18" id="Page_18">[Pg 18]</a></span></p> + + + +<hr style="width: 65%;" /> +<h2>CHAPTER III.</h2> + +<h3>OBSERVATIONS.</h3> + + +<p>In sketching out a system of observation having especial reference to +atmospheric waves and rotatory storms, regard has been had—<i>first</i>, to +the instruments that should be used, the observations to be made with +them, the corrections to be applied to such observations, and the form +of registry most suitable for recording the results: <i>second</i>, to the +times of observation: <i>third</i>, to the more important localities that +should be submitted to additional observation: <i>fourth</i>, to peculiar +phænomena requiring extraordinary observations for their elucidation: +and <i>fifth</i>, to particular seasons, when the instruments should be +watched with more than ordinary care.</p> + +<p>The more important objects of observation having especial reference to +atmospheric waves are those points which have been termed <i>crests</i> and +<i>troughs</i>. These are simply the <i>highest</i> and <i>lowest</i> readings of the +barometer, usually designated <i>maxima</i> and <i>minima</i>, and should for the +object in view receive particular attention. Whenever there is reason to +believe that the barometer is approaching either a <i>maximum</i> or +<i>minimum</i>, additional observations should be resorted to, so as to +secure as nearly as possible <i>the precise time</i> as reckoned at the ship, +with her position, of its occurrence, as well as the altitude of the +mercurial column at that time and place. By means of such ob<span class='pagenum'><a name="Page_19" id="Page_19">[Pg 19]</a></span>servations +as these on board several ships scattered over the surfaces of our great +oceans, much valuable information may be accumulated of a character +capable of throwing considerable light on the <i>direction</i> in which the +lines of barometric maxima and minima stretch, and also a tolerably +accurate notion may be formed of their progress, both as regards +direction and rate. In immediate connexion with such observations +particular attention should be paid to the direction of the wind +according to the season.</p> + + +<h4>SECTION I.—INSTRUMENTS.</h4> + +<p><i>Description and Position of Instruments.</i>—The principal instrument +requisite in these observations is the barometer, which should be of the +marine construction, and as nearly alike as possible to those furnished +to the Antarctic expedition which sailed under the command of Sir James +Clark Ross. These instruments were similar to the ordinary portable +barometers, and differed from them only in the mode of their suspension +and the necessary contraction of the tubes to prevent oscillation from +the motion of the ship. The barometer on shipboard should be suspended +on a gimbal frame, which ought not to swing too freely, but rather so as +to deaden oscillations by some degree of friction. To the upper portion +of the tube in this construction of instrument light is alike accessible +either in front or behind, and the vernier is furnished with a back and +front edge, both being in precisely the same plane, nearly embracing the +tube, and sliding up and down it by the motion of rack-work; by<span class='pagenum'><a name="Page_20" id="Page_20">[Pg 20]</a></span> the +graduation of the scale and vernier the altitude of the mercury can be +read off to ·002 inch.</p> + +<p>When the barometer is placed in the ship, its position should be as near +midships as possible, out of the reach of sunshine, but in a good light +for reading, and in a situation in which it will be but little liable to +sudden gusts of wind and changes of temperature. Great care should be +taken to ascertain the exact height of its cistern above the water-line, +and in order to facilitate night observations every possible arrangement +should be made for placing behind it a light screened by white paper.</p> + +<p><i>Observations.</i>—The first thing to be done is the reading off and +recording the temperature indicated by the thermometer that in this +construction of instrument dips into the mercury in the cistern. Sir +John Herschel has suggested that "the bulb of the thermometer should be +so situated as to afford the best chance of its indicating the exact +mean of the whole barometric column, that is to say, fifteen inches +above the cistern enclosed within the case of the barometer, nearly in +contact with its tube, and with a stem so long as to be read off at the +upper level."</p> + +<p>Previous to making an observation with the barometer the instrument +should be slightly tapped to free the mercury from any adhesion to the +glass; any violent oscillation should, however, be carefully avoided. +The vernier should then be adjusted to the upper surface of the mercury +in the tube; for this purpose its back and front edges should be made to +coincide, that is, the eye should be placed in exactly the same plane +which passes through the edges; they should then be brought carefully +down until they form a tangent with the curve produced<span class='pagenum'><a name="Page_21" id="Page_21">[Pg 21]</a></span> by the convex +surface of the mercury and the light is <i>just</i> excluded from between +them and the point of contact. It is desirable in making this adjustment +that the eye should be assisted by a magnifying-glass. The reading of +the scale should then be taken and entered in the column appropriated to +it in the proper form. If the instrument have no tubular or double-edged +index, the eye should be placed carefully at the level of the upper +surface of the mercury and the index of the vernier brought gently down +to the same level so as apparently just to touch the surface, great care +being taken that the eye index and surface of the mercury are all in the +same plane.</p> + +<p>Each observation of the barometer should be accompanied by an +observation of the direction of the wind, which should be noted in the +usual manner in which it is observed at sea. In connexion with the +<i>direction</i> the <i>force</i> of the wind should be recorded in accordance +with the following scale, contrived by Admiral Sir Francis Beaufort:—</p> + + + +<table border="0" cellpadding="1" width="80%" cellspacing="0" summary="Barometer readings in connection with the force and direction of the wind"> + +<tr> +<td>0.</td> +<td>Calm</td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +</tr> +<tr> +<td>1.</td> +<td>Light air</td> +<td> </td> +<td>or just sufficient to give steerage way.</td> +<td> </td> +<td> </td> +</tr> +<tr> +<td>2.</td> +<td>Light breeze</td> +<td>{</td> +<td>or that in which a well-conditioned</td> +<td>}</td> +<td>1 to 2 knots.</td> +</tr> + +<tr> +<td>3.</td> +<td>Gentle breeze</td> +<td>{</td> +<td>man of war,</td> +<td>}</td> +<td>3 to 4 knots.</td> +</tr> + +<tr> +<td>4.</td> +<td>Moderate breeze</td> +<td>{</td> +<td>with all sail set, and clean full,</td> +<td>}</td> +<td>5 to 6 knots.</td> +</tr> + +<tr> +<td> </td> +<td> </td> +<td>{</td> +<td>would go in smooth water from.</td> +<td>}</td> +<td> </td> +</tr> + +<tr> +<td>5.</td> +<td>Fresh breeze</td> +<td>}</td> +<td> </td> +<td>{</td> +<td>Royals, &c.</td> +</tr> + +<tr> +<td>6.</td> +<td>Strong breeze</td> +<td>}</td> +<td> </td> +<td>{</td> +<td>Single-reefed top-sails</td> +</tr> + +<tr> +<td> </td> +<td> </td> +<td>}</td> +<td> </td> +<td>{</td> +<td>and top-gallant sails.</td> +</tr> + +<tr> +<td>7.</td> +<td>Moderate gale</td> +<td>}</td> +<td>or that in which such a</td> +<td>{</td> +<td>Double-reefed top-sails,</td> +</tr> + +<tr> +<td> </td> +<td> </td> +<td>}</td> +<td>ship could just carry in</td> +<td>{</td> +<td>jib, &c.</td> +</tr> + +<tr> +<td>8.</td> +<td>Fresh gale</td> +<td>}</td> +<td>chase full and by ...</td> +<td>{</td> +<td>Triple-reefed top-sails,</td> +</tr> + +<tr> +<td> </td> +<td> </td> +<td>}</td> +<td> </td> +<td>{</td> +<td>&c. Close-reefed</td> +</tr> + +<tr> +<td>9.</td> +<td>Strong gale</td> +<td>}</td> +<td> </td> +<td>{</td> +<td>top-sails and courses.<span class='pagenum'><a name="Page_22" id="Page_22">[Pg 22]</a></span></td> +</tr> + +<tr> +<td>10.</td> +<td>Whole gale</td> +<td> </td> +<td>or that with which she could scarcely bear</td> +<td> </td> +<td> </td> +</tr> + +<tr> +<td> </td> +<td> </td> +<td> </td> +<td>close-reefed main topsail and reefed foresail.</td> +<td> </td> +<td> </td> +</tr> + +<tr> +<td>11.</td> +<td>Storm</td> +<td> </td> +<td>or that which reduces her to storm staysails.</td> +<td> </td> +<td> </td> +</tr> + +<tr> +<td>12.</td> +<td>Hurricane</td> +<td> </td> +<td>or that which no canvas could withstand.</td> +<td> </td> +<td> </td> +</tr> +</table> + + +<p><i>Corrections.</i>—As soon after the observations have been made as +circumstances will permit, the reading of the barometer should be +<i>corrected</i> for the relation existing between the capacities of the tube +and cistern (if its construction be such as to require that correction), +and for the capillary action of the tube; and then <i>reduced</i> to the +standard temperature of 32° Fahr., and to the sea-level, if on +shipboard. For the first correction the <i>neutral point</i> should be marked +upon each instrument. It is that particular height which, in its +construction, has been actually measured from the surface of the mercury +in the cistern, and indicated by the scale. In general the mercury will +stand either above or below the neutral point; if <i>above</i>, a portion of +the mercury must have left the cistern, and consequently must have +<i>lowered</i> the surface in the cistern: in this case the altitude as +measured by the scale will be <i>too short—vice versâ</i>, if below. The +relation of the capacities of the tube and cistern should be +experimentally ascertained, and marked upon the instrument by the maker. +Suppose the capacity to be 1/50, marked thus on the instrument, +"<i>Capacity 1/50:</i>" this indicates that for every inch of variation of +the mercury in the tube, that in the cistern will vary contrariwise +1/50th of an inch. When the mercury in the tube is <i>above</i> the neutral +point, the difference between it and the neutral point is to be reduced +in the proportion expressed by the "capacity" (in the case supposed, +divided by 50), and<span class='pagenum'><a name="Page_23" id="Page_23">[Pg 23]</a></span> the quotient <i>added</i> to the observed height; if +<i>below, subtracted</i> from it. In barometers furnished with a fiducial +point for adjusting the lower level, this correction is superfluous, and +must not be applied.</p> + +<p>The second correction required is for the capillary action of the tube, +the effect of which is always to depress the mercury in the tube by a +certain quantity inversely proportioned to the diameter of the tube. +This quantity should be experimentally determined during the +construction of the instrument, and its amount marked upon it by the +maker, and is always to be <i>added</i> to the height of the mercurial +column, previously corrected as before. For the convenience of those who +may have barometers, the capillary action of which has not been +determined, a table of corrections for tubes of different diameters is +placed in the Appendix, Table I.</p> + +<p>The next correction, and in some respects the most important of all, is +that due to the temperature of the mercury in the barometer tube at the +time of observation, and to the expansion of the scale. Table II. of the +Appendix gives for every degree of the thermometer and every half-inch +of the barometer, the proper quantity to be added or subtracted for the +reduction of the observed height to the standard temperature of the +mercury at 32° Fahr.</p> + +<p>After these the index correction should be applied. This is the amount +of difference between the particular instrument and the readings of the +Royal Society's flint-glass barometer when properly corrected, and is +generally known as the <i>zero</i>. It is impossible to pay too much +attention to the determination of this point. For this<span class='pagenum'><a name="Page_24" id="Page_24">[Pg 24]</a></span> purpose, when +practicable, the instrument should be immediately compared with the +Royal Society's standard, and the difference of the readings of both +instruments, when corrected as above, carefully noted and preserved. +Where, however, this is impracticable, the comparison should be effected +by means either of some other standard previously so compared, or of an +intermediate portable barometer, the zero point of which has been <i>well +determined</i>. Suspend the portable barometer as near as convenient to the +ship's barometer, and after at least an hour's quiet exposure, take as +many readings of both instruments as may be necessary to reduce the +probable error of the mean of the differences below 0.001 inch. Under +these circumstances the mean difference of all the readings will be the +<i>relative</i> zero or index error, whence, if that of the intermediate +barometer be known, that of the other may be found. As such comparisons +will always be made when the vessel is in port, sufficient time can be +allowed for making the requisite number of observations: hourly readings +would perhaps be best, and they would have the advantage of forming part +of the system when in operation, and might be accordingly used as such.</p> + +<p>It is not only desirable that the zero point of the barometer should be +well determined in the first instance; it should also be carefully +verified on every opportunity which presents itself; and in every +instance, previous to sailing, it should be re-compared with the +standard on shore by the intervention of a portable barometer, and no +opportunity should be lost of comparing it on the voyage by means of +such an intermediate instrument with the standard baro<span class='pagenum'><a name="Page_25" id="Page_25">[Pg 25]</a></span>meters at St. +Helena, the Cape of Good Hope, Bombay, Madras, Paramatta, Van Diemen's +Island, and with any other instruments likely to be referred to as +standards, or employed in research elsewhere. Any vessel having a +portable barometer on board, the zero of which has been well determined, +would do well, on touching at any of the ports above named, to take +comparative readings with the standards at those ports, and record the +differences between the standard, the portable, and the ship barometers. +By such means the zero of one standard may be transported over the whole +world, and those of others compared with it ascertained. To do so, +however, with perfect effect, will require that the utmost care should +be taken of the portable barometer; it should be guarded as much as +possible from all accident, and should be kept safely in the "portable" +state when not immediately used for comparison. To transport a +well-authenticated zero from place to place is by no means a point of +trifling importance. Neither should it be executed hurriedly nor +negligently. Some of the greatest questions in meteorology depend on its +due execution, and the objects for which these instructions have been +prepared will be greatly advanced by the zero points of all barometers +being referred to one common standard. Upon the arrival of the vessel in +England, at the termination of the voyage, the ship's barometer should +be again compared with the same standard with which it was compared +previous to sailing; and should any difference be found, it should be +most carefully recorded.</p> + +<p>The correction for the height of the cistern <i>above</i> or <i>below</i> the +water-line is <i>additive</i> in the former case,<span class='pagenum'><a name="Page_26" id="Page_26">[Pg 26]</a></span> <i>subtractive</i> in the +latter. Its amount may be taken, nearly enough, by allowing 0·001 in. of +the barometer for each foot of difference of level.</p> + +<p>An example of the application of these several corrections is +subjoined:—</p> + + + +<table border="0" cellpadding="1" width="65%" cellspacing="0" summary="Height of the cistern above and below the water line"> +<tr> +<th colspan="2"><i>Attached Therm</i>. 54°·3.</th> +</tr> +<tr> +<td>Barometer reading</td> +<td align='right'>29·409</td> +</tr> +<tr> +<td>Corr. for capacity</td> +<td align='right'>- ·017</td> +</tr> +<tr> +<td> </td> +<td align='right'>———</td> +</tr> +<tr> +<td> </td> +<td align='right'>29·392</td> +</tr> +<tr> +<td>Corr. for capillarity</td> +<td align='right'>+ ·032</td> +</tr> +<tr> +<td> </td> +<td align='right'>———</td> +</tr> +<tr> +<td> </td> +<td align='right'>29·424</td> +</tr> +<tr> +<td>Corr. for temperature</td> +<td align='right'>- ·068</td> +</tr> +<tr> +<td> </td> +<td align='right'>———</td> +</tr> +<tr> +<td> </td> +<td align='right'>29·356</td> +</tr> +<tr> +<td>Corr. for zero and water-line</td> +<td align='right'>+ ·040</td> +</tr> +<tr> +<td> </td> +<td align='right'>———</td> +</tr> +<tr> +<td>Aggregate = pressure at</td> +<td> </td> +</tr> +<tr> +<td>sea-level</td> +<td align='right'>29·396</td> +</tr> +<tr> +<td> </td> +<td align='right'>———</td> +</tr> +<tr> +<th colspan="2"><i>Data for the correction of the Instrument.</i></th> +</tr> +<tr> +<td>Neutral point</td> +<td align='right'>30·123</td> +</tr> +<tr> +<td>Capacity 1/42</td> +<td> </td> +</tr> +<tr> +<td>Capillary action</td> +<td align='right'>+ ·032</td> +</tr> +<tr> +<td>Zero to Royal Society</td> +<td align='right'>+ ·036</td> +</tr> +<tr> +<td>Corr. for altitude above</td> +<td> </td> +</tr> +<tr> +<td>water line</td> +<td align='right'>+ ·004</td> +</tr> +</table> + +<p>It would greatly facilitate the comparison of the barometric +observations by projecting them in curves when all the proper +corrections have been applied. This may be accomplished by a much +smaller expenditure of time than may at first be supposed. A paper of +engraved squares on which the observations of twelve days may be laid +down on double the natural scale, would be very suitable for the +purpose.<a name="FNanchor_4_4" id="FNanchor_4_4"></a><a href="#Footnote_4_4" class="fnanchor">[4]</a> The projection of each day's observations would occupy but a +short time; and should circumstances on any occasion prevent the +execution of it, when the ship was becalmed or leisure otherwise +afforded, it would form an interesting and useful occupation, and<span class='pagenum'><a name="Page_27" id="Page_27">[Pg 27]</a></span> serve +to beguile some of the tedium often experienced at such intervals.</p> + +<p><i>Registers.</i>—For the particular object in view the register need not be +very extensive. One kept in the annexed form will be amply sufficient. +It should, however, be borne in mind that none but <i>uncorrected</i> +observations should find admission; in point of fact it should be +strictly a register of phænomena as <i>observed</i>, and on no account +whatever should any entry be made from recollection, or any attempt made +to fill up a blank by the apparent course of the numbers before and +after. The headings of the columns will, it is hoped, be sufficiently +explicit. It is desirable in practice that the column for remarks should +embrace an entire page opposite the other entries, in order that +occasional observations, as well as several other circumstances +continually coming under review in the course of keeping a journal, may +find entry.</p> + +<table border="1" cellpadding="10" width="100%" cellspacing="0" summary="Meteorological Register"> +<tr> +<th colspan="10">METEOROLOGICAL REGISTER kept on board ——— during her<br /> +voyage from ——— to ——— by ——— </th></tr> +<tr> +<th colspan="2" align="center" rowspan="2">Date.</th> +<th rowspan="2">Lat.</th> +<th rowspan="2">Long.</th> +<th rowspan="2">Barom.</th> +<th rowspan="2">Att. Ther.</th> +<th colspan="2" align="center">Wind.</th> +<th rowspan="2">Remarks.</th> +<th rowspan="2">Observer.</th> +</tr> + +<tr> +<th>Direction.</th> +<th>Force.</th> +</tr> +<tr> +<td> </td> +<td>h .m.</td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +</tr> + +<tr> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +</tr> + +<tr> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +</tr> + +<tr> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +<td> </td> +</tr> +</table> + + +<p>The only difference between the above form and one for the reception of +<i>corrected</i> readings will be the dispensing with the column for the +attached thermometer, and placing under the word Barom. "corrected."<span class='pagenum'><a name="Page_28" id="Page_28">[Pg 28]</a></span></p> + +<h4>II.—TIMES OF OBSERVATION.</h4> + +<p>There can be no question that the greatest amount of information, the +accuracy of the data supplied, and in fact every meteorological element +necessary to increase our knowledge of atmospheric waves, may be best +obtained by an uninterrupted series of <i>hourly</i> observations made on +board vessels from their leaving England until their safe arrival again +at the close of their respective voyages; but from a variety of +circumstances—the nature of the service in which the vessels may be +employed, particular states of the weather, &c.—such a course of +unremitting labour cannot be expected; it is therefore necessary to fix +on some stated hours at which the instruments before particularized +should be regularly observed throughout the voyage, and their +indications faithfully recorded. The hours of 3 A.M., 9 A.M., 3 P.M., +and 9 P.M., are now so generally known as <i>meteorological hours</i>, that +nothing should justify a departure from them; and it is the more +essential that these hours should be adopted in the present inquiry, +because the series of observations made at intervals terminated by these +hours can the more readily be used in connexion with those made +contemporaneously on land, and will also serve to carry on +investigations previously instituted, and which have received +considerable illustration by means of observations at the regular +meteorological hours; we therefore recommend their general adoption in +all observations conducted at sea.</p> + +<p>It is intended in the sequel to call attention to particular parts of +the earth's surface where it is desirable that additional observations +should be made, in order to<span class='pagenum'><a name="Page_29" id="Page_29">[Pg 29]</a></span> furnish data of a more accurate character, +and to mark more distinctly barometric changes than the four daily +readings are capable of effecting. The best means of accomplishing this +for the object in view appears to be the division of the interval of six +hours into two equal portions, and to make the necessary observations +eight times in the course of twenty-four hours. In the particular +localities to which allusion has been made we recommend the following as +the hours of observation:—</p> + +<p>A.M. 3, 6, 9, noon. P.M. 3, 6, 9, midnight.</p> + +<p>In other localities besides those hereafter to be mentioned, when +opportunities serve, readings at these hours would greatly enhance the +value of the four daily readings.</p> + +<p>There are, however, portions of the surface of our planet, and probably +also phænomena that occur in its atmosphere, which require still closer +attention than the eight daily readings. One such portion would appear +to exist off the western coast of Africa, and we recommend the adoption +of <i>hourly</i> readings while sailing to the westward of this junction of +aqueous and terrestrial surface; more attention will be directed to this +point as we proceed. There are also phænomena the localities of which +may be undetermined, and the times of their occurrence unknown, but so +important a relation do they bear to the subject of our inquiries, that +they demand the closest attention. They will be more particularly +described under the head of accumulations of pressure preceding and +succeeding storms, and minute directions given for the hourly +observations of the necessary instruments. In<span class='pagenum'><a name="Page_30" id="Page_30">[Pg 30]</a></span> the mean time we may here +remark that hourly observations under the circumstances above alluded to +are the more important when we consider that the barometer, the +instrument employed in observing these moving atmospheric masses, is +itself in motion. The ship may meet the accumulation of pressure and +sail through it transversely; or she may sail along it, the course of +the vessel being parallel to the line marking the highest pressure, the +ridge or crest of the wave; or the ship may make any angle with this +line: but whatever the circumstances may be under which she passes +through or along with such an accumulation of pressure, it should ever +be borne in mind that her position on the earth's surface is scarcely +ever the same at any one observation as it was at the preceding, the +barometer in the interval has changed <i>its</i> position as well as the line +of maximum pressure, the rate of progress of which it is desirable to +observe. It will, therefore, be at once apparent that in order to obtain +the most accurate data on this head hourly observations are +indispensable. To these readings should of course be appended the places +of the ship from hour to hour, especially if she alter her course much.</p> + +<p>There is another point to which we wish to call attention in immediate +connexion with hourly readings—it is the observation of the instruments +on the days fixed for that purpose: they were originally suggested by +Sir John Herschel, whose directions should be strictly attended to: they +are as follows:—</p> + +<p>The days fixed upon for these observations are the 21st of March, the +21st of June, the 21st of September, and the 21st of December, being +those, or immediately ad<span class='pagenum'><a name="Page_31" id="Page_31">[Pg 31]</a></span>joining to those of the equinoxes and +solstices, in which the <i>solar influence</i> is either stationary or in a +state of most rapid variation. <i>But should any one of those 21st days +fall on a Sunday, then it will be understood that the observations are +to be deferred till the next day, the 22nd.</i> The series of observations +on board each vessel should commence at 6 o'clock A.M. of the appointed +days, and terminate at 6 A.M. of the days following, according to the +usual reckoning of time adopted in the daily observations.</p> + +<p>In addition to the twenty-five hourly readings at the solstices and +equinoxes as above recommended, it would be desirable to continue the +observations until a complete elevation and depression of the barometer +had been observed at these seasons. This plan is adopted at the Royal +Observatory, Greenwich, and would be attended with this advantage were +it generally so—the progress of the elevation and depression would be +more readily traced and their velocities more accurately determined than +from the four or eight daily readings.</p> + +<hr style='width: 45%;' /> + + +<h4>III.—LOCALITIES FOR ADDITIONAL OBSERVATIONS.</h4> + +<p>In sketching out a system of barometric observation having especial +reference to the acquisition of data from which the <i>barometric +character</i> of certain large areas of the surface of the globe may be +determined—inasmuch as such areas are distinguished from each other, on +the one hand by consisting of extensive spaces of the oceanic surface +unbroken, or scarcely broken, by land; on the other by the proximity of +such oceanic surface to large<span class='pagenum'><a name="Page_32" id="Page_32">[Pg 32]</a></span> masses of land, and these masses +presenting two essentially different features, the one consisting of +land particularly characterized as continental, the other as insular, +regard has been accordingly had to such distribution of land and water.</p> + +<p>As these instructions have especial reference to observations at sea, +observations on land have not been alluded to; but in order that the +data accumulated may possess that value which is essential for carrying +on the inquiry in reference to atmospheric waves with success, provision +is made to mark out more distinctly the barometric effects of the +junction of large masses of land and water. It is well known that the +oceanic surface, and even the smaller surfaces of inland seas, produce +decided inflexions of the isothermal lines. They exercise an important +influence on temperature. It has also been shown that the neighbourhood +of water has a very considerable influence in increasing the +oscillations of the mercurial column in the barometer, and in the great +systems of European undulations it is well known that these oscillations +increase especially towards the north-west. The converse of this, +however, has not yet been subjected to observation; there has been no +systematic co-operation of observers for the purpose of determining the +barometric affections of large masses of water, such as the central +portion of the basin of the northern Atlantic, the portion of oceanic +surface between the Cape of Good Hope and Cape Horn, the Indian and +Southern oceans, and the vast basin of the Pacific. Nor are we yet +acquainted with the character of the oscillations, whether increasing or +decreasing, as we recede from the central portions of the oceanic +surfaces<span class='pagenum'><a name="Page_33" id="Page_33">[Pg 33]</a></span> we have mentioned towards the land which forms their eastern, +western, or northern boundaries. This influence of the junction line of +land and water, so far as it is yet known, has been kept in view in +framing these instructions, and, as it appears so prominently in Europe, +it is hoped the additional observations between the four daily readings +to which probably many observers may habitually restrict themselves, +making on certain occasions and in particular localities a series of +observations at intervals of three hours, will not be considered too +frequent when the great importance of the problem to be solved is fully +apprehended. It need scarcely be said that the value of these +observations at three-hourly intervals will be greatly increased by the +number of observers co-operating in them. Upon such an extensive system +of co-operation a large space on the earth's surface, possessing +peculiarities which distinguish it from others extremely unlike it in +their general character, or assimilate it to such as possess with it +many features in common, is marked out below for particular observation, +occupying more than two-thirds of a zone in the northern hemisphere, +having a breadth of 40°, and including every possible variety of +terrestrial and aqueous surface, from the burning sands of the great +African desert, situated about the centre, to the narrow strip of land +connecting the two Americas on the one side, and the chain of islands +connecting China and Hindostan with Australia on the other. On each side +of the African continent we have spaces of open sea between 30° and 40° +west longitude north of the equator, and between 60° and 80° east +longitude, in or to the south of the equator, admirably suited for +contrasting the barometric affections,<span class='pagenum'><a name="Page_34" id="Page_34">[Pg 34]</a></span> as manifested in these spaces of +open water, with those occurring in situations where the influence of +the terrestrial surface comes into more active operation.</p> + +<p>The localities where three-hourly readings are chiefly desirable may be +specified under the heads of <i>Northern Atlantic, Southern Atlantic, +Indian</i> and <i>Southern Oceans,</i> and <i>Pacific Ocean</i>.</p> + +<p><br /></p> + +<p><i>Northern Atlantic. Homeward-bound Voyages.</i>—The discussion of +observations made in the United Kingdom and the western border of +central Europe, has indicated that off the north-west of Scotland a +centre of great barometric disturbance exists. This centre of +disturbance appears to be considerably removed from the usual tracks of +vessels crossing the Atlantic; nevertheless some light may be thrown on +the barometric phænomena resulting from this disturbance by observations +during homeward-bound voyages, especially after the vessels have passed +the meridian of 50° west longitude. Voyagers to or from Baffin and +Hudson bays would do well during the whole of the voyage to read off the +barometer every three hours, as their tracks would approach nearest the +centre of disturbance in question. Before crossing the 50th meridian, +the undulations arising from the distribution of land and water in the +neighbourhood of these vast inland seas would receive considerable +elucidation from the shorter intervals of observation, and after passing +the 50th meridian the extent of undulation, as compared with that +observed by the more southerly vessels, would be more distinctly marked +by the three-hourly series. Surveying vessels stationed on the +north-western coasts of Ireland and<span class='pagenum'><a name="Page_35" id="Page_35">[Pg 35]</a></span> Scotland may contribute most +important information on this head by a regular and, as far as +circumstances will allow, an uninterrupted series either of six-hourly +or three-hourly observations. The intervals of observation on board +vessels stationed at the Western Isles, the Orkneys, and the Shetland +Isles, ought not to be longer than <i>three</i> hours, principally on account +of the great extent of oscillation observed in those localities. Vessels +arriving from all parts of the world as they approach the United Kingdom +should observe at shorter intervals than six hours. As a general +instruction on this head the series of three-hourly observations may be +commenced on board vessels from America and the Pacific by the way of +Cape Horn on their passing the 20th meridian, such three-hourly +observations to be continued until the arrival of the vessels in port. +Ships by the way of the Cape of Good Hope should commence the +three-hourly series either on leaving or passing the colony, in order +that the phænomena of the tropical depression hereafter to be noticed +may be well observed.</p> + +<p><br /></p> + +<p><i>Northern Atlantic. Outward-bound Voyages</i>.—Vessels sailing to the +United States, Mexico, and the West Indies, should observe at three +hours' interval upon passing the 60th meridian. Observations at this +interval, on board vessels navigating the Gulf of Mexico and the +Caribbean Sea, will be particularly valuable in determining the extent +of oscillation as influenced by the masses of land and water in this +portion of the torrid zone, as compared with the oscillation noticed off +the western coast of Africa, hereafter to be referred to.<span class='pagenum'><a name="Page_36" id="Page_36">[Pg 36]</a></span></p> + +<p><br /></p> + +<p><i>Southern Atlantic. Outward and homeward bound</i>.—Without doubt the most +interesting phænomenon, and one that lies at the root of the great +atmospheric movements, especially those proceeding northwards in the +northern hemisphere and southwards in the southern, is the equatorial +depression first noticed by Von Humboldt and confirmed by many observers +since. We shall find the general expression of this most important +meteorological fact in the Report of the Committee of Physics and +Meteorology, appointed by the Royal Society in 1840, as follows: "The +barometer, at the level of the sea, does not indicate a mean atmospheric +pressure of equal amount in all parts of the earth; but, on the +contrary, the equatorial pressure is uniformly less in its mean amount +than at and beyond the tropics." Vessels that are outward bound should, +upon passing 40° north latitude, commence the series of three-hourly +observations, with an especial reference to the equatorial depression. +These three-hourly observations should be continued until the latitude +of 40° south has been passed: the whole series will then include the +minimum of the depression and the two maxima or apices forming its +boundaries. (See Daniell's 'Meteorological Essays,' 3rd edition.) In +passages across the equator, should the ships be delayed by calms, +opportunities should be embraced for observing this depression with +greater precision by means of <i>hourly</i> readings; and these readings will +not only be valuable as respects the depression here spoken of, but will +go far to indicate the character of any disturbance that may arise, and +point out, as nearly as such observations will allow, the precise time +when such disturbance produced its effects in the neighbourhood of<span class='pagenum'><a name="Page_37" id="Page_37">[Pg 37]</a></span> the +ships. In point of fact they will clearly illustrate the diversion of +the tendency to rise, spoken of in the Report before alluded to, as +resulting in ascending columns and sheets, between which wind flaws, +capricious in their direction and intensity, and often amounting to +sharp squalls, mark out the course of their feeders and the indraft of +cooler air from a distance to supply their void. Hourly observations, +with especial reference to this and the following head of inquiry, +should also be made off the western coast of Africa during the +homeward-bound voyage.</p> + +<p>Immediately connected with this part of the outward-bound voyage, hourly +observations, as often as circumstances will permit, while the ships are +sailing from the Madeiras to the equator, will be extremely valuable in +elucidating the origin of the great system of south-westerly atmospheric +waves that traverse Europe, and in furnishing data for comparison with +the amount of oscillation and other barometric phænomena in the Gulf of +Mexico and the Caribbean Sea, a portion of the torrid zone essentially +different in its configuration and in the relations of its area to land +and water, as contra-distinguished to the northern portion of the +African continent; and these hourly observations are the more desirable +as the vessels may approach the land. They may be discontinued on +passing the equator, and the three-hourly series resumed.</p> + +<p>There are two points in the southern hemisphere, between 80° west +longitude and 30° east longitude, that claim particular attention in a +barometric point of view, viz., Cape Horn and the Cape of Good Hope; the +latter is within the area marked out for the three-hourly obser<span class='pagenum'><a name="Page_38" id="Page_38">[Pg 38]</a></span>vations, +and too much attention cannot be paid to the indications of the +barometer as vessels are approaching or leaving the Cape. The northern +part of the South Atlantic Ocean has been termed the <i>true Pacific Ocean +of the world</i>; and at St. Helena a gale was scarcely ever known; it is +also said to be entirely free from actual storms (Col. Reid's 'Law of +Storms,' 1st edition, p. 415). It may therefore be expected that the +barometer will present in this locality but a small oscillation, and +ships in sailing from St. Helena to the Cape will do well to ascertain, +by means of the three-hourly observations, the increase of oscillation +as they approach the Cape. The same thing will hold good with regard to +Cape Horn: it appears from previous observation that a permanent +barometric depression exists in this locality, most probably in some way +connected with the immense depression noticed by Captain Sir James Clark +Ross, towards the Antarctic Circle. The general character of the +atmosphere off Cape Horn is also extremely different from its character +at St. Helena. It would therefore be well for vessels sailing into the +Pacific by Cape Horn, to continue the three-hourly observations until +the 90th meridian is passed.</p> + +<p>Before quitting the Atlantic Ocean it may be well to notice the marine +stations mentioned in my Third Report on Atmospheric Waves,<a name="FNanchor_5_5" id="FNanchor_5_5"></a><a href="#Footnote_5_5" class="fnanchor">[5]</a> as being +particularly suitable for testing the views advanced in that report and +for tracing a wave of the south-westerly system from the most western +point of Africa to the extreme north of Europe. A series<span class='pagenum'><a name="Page_39" id="Page_39">[Pg 39]</a></span> of hourly +observations off the western coast of Africa has already been suggested. +Vessels staying at Cape Verd Islands should not omit to make +observations at three hours' interval <i>during the whole of their stay</i>, +and when circumstances will allow, hourly readings. At the Canaries, +Madeiras, and the Azores, similar observations should be made. Vessels +touching at Cape Cantin, Tangier, Gibraltar, Cadiz, Lisbon, Oporto, +Corunna, and Brest, should also make these observations while they are +in the localities of these ports. At the Scilly Isles we have six-hourly +observations, made under the superintendence of the Honourable the +Corporation of the Trinity House. Ships in nearing these islands and +making the observations already pointed out, will greatly assist in +determining the increase of oscillation proceeding westward from the +nodal point of the two great European systems. We have already mentioned +the service surveying vessels employed on the coasts of Ireland and +Scotland may render, and the remaining portion of the area marked out in +the report may be occupied by vessels navigating the North Sea and the +coast of Norway, as far as Hammerfest.</p> + +<p>In connexion with these observations, having especial reference to the +European system of south-westerly atmospheric waves, the Mediterranean +presents a surface of considerable interest, both as regards these +particular waves, and the influence its waters exert in modifying the +two great systems of central Europe. The late Professor Daniell has +shown from the Manheim observations, that small undulations, having +their origin on the northern borders of the Mediterranean, have +propagated themselves<span class='pagenum'><a name="Page_40" id="Page_40">[Pg 40]</a></span> northward, and in this manner, but in a smaller +degree, the waters of the Mediterranean have contributed to increase the +oscillation as well as the larger surface of the northern Atlantic. In +most of the localities of this great inland sea six-hourly observations +may suffice for this immediate purpose; but in sailing from Lisbon +through the Straits of Gibraltar, in the neighbourhood of Sicily and +Italy, and in the Grecian Archipelago, we should recommend the +three-hourly series, as marking more distinctly the effects resulting +from the proximity of land; this remark has especial reference to the +passage through the Straits of Gibraltar, where, if possible, hourly +observations should be made.</p> + +<p><br /></p> + +<p><i>The Indian and Southern Oceans. Outward and homeward bound.</i>—On +sailing from the Cape of Good Hope to the East Indies, China, or +Australia, observations at intervals of three hours should be made until +the 40th meridian east is passed (homeward-bound vessels should commence +the three-hourly readings on arriving at this meridian). Upon leaving +the 40th meridian the six-hourly observations may be resumed on board +vessels bound for the Indies and China until they arrive at the equator, +when the readings should again be made at intervals of three hours, and +continued until the arrival of the vessels in port. With regard to +vessels bound for Australia and New Zealand, the six-hourly readings may +be continued from the 40th to the 100th meridian, and upon the vessels +passing the latter, the three-hourly readings should be commenced and +continued until the vessels arrive in port. Vessels navigating the +Archipelago<span class='pagenum'><a name="Page_41" id="Page_41">[Pg 41]</a></span> between China and New Zealand, should make observations +every three hours, in order that the undulations arising from the +configuration of the terrestrial and oceanic surfaces may be more +distinctly marked and more advantageously compared with the Gulf of +Mexico, the Caribbean Sea, and the northern portion of the African +continent.</p> + +<p><br /></p> + +<p><i>The Pacific Ocean.</i>—As this ocean presents so vast an aqueous surface, +generally speaking observations at intervals of six hours will be amply +sufficient to ascertain its leading barometric phænomena. Vessels, +however, on approaching the continents of North and South America, or +sailing across the equator, should resort to the three-hourly readings, +in order to ascertain more distinctly the effect of the neighbourhood of +land on the oscillations of the barometer, as generally observed, over +so immense a surface of water in the one case, and the phænomena of the +equatorial depression in the other: the same remarks relative to the +latter subject, which we offered under the head of South Atlantic, will +equally apply in the present instance. The configuration of the western +shores of North America renders it difficult to determine the precise +boundary where the three-hourly series should commence; the 90th +meridian is recommended for the boundary as regards South America, and +from this a judgment may be formed as to where the three-hourly +observations should commence in reference to North America.</p> + +<p><br /></p> + +<p>In the previous sketch of the localities for the more important +observations, it will be seen that within the<span class='pagenum'><a name="Page_42" id="Page_42">[Pg 42]</a></span> tropics there are three +which demand the greatest regard.</p> + +<p>I. The Archipelago between the two Americas, more particularly comprised +within the 40th and 120th meridians west longitude, and the equator and +the 40th degree of north latitude. As a general principle we should say +that vessels within this area should observe the barometer every three +hours. Its eastern portion includes the lower branches of the storm +paths, and on this account is peculiarly interesting, especially in a +barometric point of view.</p> + +<p>II. <i>The Northern portion of the African Continent, including the Sahara +or Great Desert.</i>—This vast radiating surface must exert considerable +influence on the waters on each side northern Africa. Vessels sailing +within the area comprised between 40° west and 70° east, and the equator +and the 40th parallel, should also make observations at intervals of +three hours.</p> + +<p>III. <i>The great Eastern Archipelago.</i>—This presents a somewhat similar +character to the western; like that, it is the region of terrific +hurricanes, and it becomes a most interesting object to determine its +barometric phænomena; the three-hourly system of observation may +therefore be resorted to within an area comprised between the 70th and +140th meridians, and the equator and the 40th degree of north latitude.</p> + +<p>The southern hemisphere also presents three important localities, the +prolongations of the three tropical areas. It is unnecessary to enlarge +upon these, as ample instructions have been already given. We may, +however, remark, with regard to Australia, that three-hourly<span class='pagenum'><a name="Page_43" id="Page_43">[Pg 43]</a></span> +observations should be made within the area comprised between the 100th +and 190th meridians east, and the equator and the 50th parallel south, +and hourly ones in the immediate neighbourhood of all its coasts.</p> + + +<h4>IV.—STORMS, HURRICANES, AND TYPHOONS.</h4> + +<p>The solution of the question—How far and in what manner are storms +connected with atmospheric waves?—must be extremely interesting to +every one engaged in either the naval or merchant service. As we have in +the former chapters directed attention to their connexion, our great +object here will be to endeavour to mark out such a line of observation +as appears most capable of throwing light, not only on the most +important desiderata as connected with storms, but also their connexion +or non-connexion with atmospheric waves. We shall accordingly +arrange this portion of the instructions under the following +heads:—<i>Desiderata</i>; <i>Localities</i>; <i>Margins</i>; <i>Preceding and Succeeding +Accumulations of Pressure.</i></p> + +<p><i>Desiderata.</i>—The most important desiderata appertaining to the subject +of storms, are certainly their origin and termination. Of these initial +and terminal points in the course of great storms we absolutely know +nothing, unless <i>the white appearance of a round form</i> observed by Mr. +Seymour on board the Judith and Esther, in lat. 17° 19' north and long. +52° 10' west (see Col. Reid's 'Law of Storms,' 1st edit. p. 65), may be +regarded as the commencement of the Antigua hurricane of August 2, 1837. +This vessel was the most eastern of those from<span class='pagenum'><a name="Page_44" id="Page_44">[Pg 44]</a></span> which observations had +been obtained; and it is the absence of contemporaneous observations to +the eastward of the 50th meridian that leaves the question as to the +origin of the West Indian revolving storms unsolved. Not one of Mr. +Redfield's storm routes extends eastward of the 50th meridian; this at +once marks out, so far as storms are concerned, the entire space +included between the 20th and 50th meridians, the equator and the 60th +parallel, as a most suitable area for observations, under particular +circumstances hereafter to be noticed, with especial reference either to +the commencement or termination of storms, or the prolongation of Mr. +Redfield's storm paths.</p> + +<p><i>Localities.</i>—The three principal localities of storms are as +follows:—I. The western portion of the basin of the North Atlantic; II. +The China Sea and Bay of Bengal; and III. The Indian Ocean, more +particularly in the neighbourhood of Mauritius. The first two have +already been marked out as areas for the three-hourly observations; to +the latter, the remark as to extra observations under the head of +Desiderata will apply.</p> + +<p><i>Margins.</i>—Mr. Redfield has shown that on some occasions storms have +been preceded by an unusual pressure of the atmosphere; the barometer +has stood remarkably <i>high</i>, and it has hence been inferred that there +has existed <i>around</i> the gale an accumulation of air forming a margin; +barometers placed under this margin indicating a much greater pressure +than the mean of the respective localities. With regard to the West +Indian and American hurricanes—any considerable increase of pressure, +especially within the space marked out to the eastward of the 50th +meridian, will demand immediate attention.<span class='pagenum'><a name="Page_45" id="Page_45">[Pg 45]</a></span> Upon the barometer ranging +<i>very high</i> within this space, three-hourly observations should be +immediately resorted to; and if possible, <i>hourly</i> readings taken, and +this is the more important the nearer the vessel may be to the 50th +meridian. Each observation of the barometer should be accompanied by an +observation of the wind—its direction should be most carefully noted, +and the force estimated according to the scale in page 21, or by the +anemometer. It would be as well <i>at the time</i> to project the barometric +readings in a curve even of a rough character, that the extent of fall +after the mercury had passed its maximum might be readily discernible by +the eye. A paper ruled in squares, the vertical lines representing the +commencement of hours, and the horizontal tenths of an inch, would be +quite sufficient for this purpose. The <i>force</i> of the wind should be +noted at, or as near to the time of the passage of the maximum as +possible. During the fall of the mercury particular attention should be +paid to the manner in which the wind changes, should any change be +observed; and should the wind continue blowing steadily in <i>one</i> +direction, but gradually <i>increasing</i> in force, then such increments of +force should be most carefully noted. During the fall of the barometer, +should the changes of the wind and its increasing force indicate the +neighbourhood of a revolving storm, (independent of the obvious reasons +for avoiding the focus of the storm,) it would contribute as much to +increase our knowledge of these dangerous vortices to keep as near as +possible to their margins as to approach their centres. The recess from +the centre towards the margin of the storm, will probably be rendered +apparent<span class='pagenum'><a name="Page_46" id="Page_46">[Pg 46]</a></span> by the <i>rising</i> of the mercury; and so far as the observations +may be considered valuable for elucidating the connexion of atmospheric +waves with rotatory storms (other motives being balanced), it might be +desirable to keep the ship near the margin—provided she is not carried +beyond the influence of the winds which characterize the latter half of +the storm—until the barometer has nearly attained its usual elevation. +By this means some notion might be formed of the general direction of +the line of barometric pressure preceding or succeeding a storm.</p> + +<p>Should a gale be observed commencing without its having been preceded by +an unusual elevation of the mercurial column, and consequently no +additional observation have been made; when the force of the wind is +noted in the usual observations at or above 5, then the three-hourly +series should be resorted to, and the same care taken in noting the +direction, changes, and force of the wind as pointed out in the +preceding paragraph.</p> + +<p>The foregoing remarks relate especially to the central and western +portions of the North Atlantic; they will however equally apply to the +remaining localities of storms. Under any circumstances, and in any +locality, a <i>high</i> barometer not less than a low one should demand +particular attention, and if possible, <i>hourly</i> readings taken some time +before and after the passage of the maximum: this will be referred to +more particularly under the next head.</p> + +<p><i>Preceding and Succeeding Accumulations of Pressure.</i>—Mr. Redfield has +shown in his Memoir of the Cuba Hurricane of October, 1844, that two +associated storms were<span class='pagenum'><a name="Page_47" id="Page_47">[Pg 47]</a></span> immediately preceded by a barometric wave, or +accumulation of pressure, the barometer rising above the usual or annual +mean. We have just referred to the importance of <i>hourly</i> observations +on occasions of the readings being <i>high</i> as capable of illustrating the +marginal phænomena of storms, and in connexion with these accumulations +of pressure in advance of storms we would reiterate the suggestion. +These strips of accumulated pressure are doubtless crests of atmospheric +waves rolling forwards. In some cases a ship in its progress may cut +them transversely in a direction at right angles to their <i>length</i>, in +others very obliquely; but in all cases, whatever section may be given +by the curve representing the observations, too much attention cannot be +bestowed on the barometer, the wet and dry bulb thermometer, the +direction and force of the wind, the state of the sky, and the +appearance of the ocean during the ship's passage <i>through</i> such an +accumulation of pressure. When the barometer attains its mean altitude, +and is rapidly rising above it in any locality, then <i>hourly</i> +observations of the instruments and phænomena above noticed should be +commenced and continued until after the mercury had attained its highest +point and had sunk again to its mean state. In such observations +particular attention should be paid to the direction and force of the +wind preceding the barometric maximum—and the same phænomena succeeding +it, and particular notice should be taken of the time when, and amount +of any change either in the direction or force of the wind. It is by +such observations as these, carried on with great care and made at every +accessible portion of the oceanic surface, that we may be able to +ascertain the continuity<span class='pagenum'><a name="Page_48" id="Page_48">[Pg 48]</a></span> of these atmospheric waves, to determine +somewhat respecting their length, to show the character of their +connexion with the rotatory storm, and to deduce the direction and rate +of their progress.</p> + +<hr style="width: 65%;" /> + +<h4>V.—SEASONS FOR EXTRA OBSERVATIONS.</h4> + + +<p>In reference to certain desiderata that have presented themselves in the +course of my researches on this subject (see Report of the British +Association for the Advancement of Science, 1846, p. 163), the <i>phases</i> +of the larger barometric undulations, and the <i>types</i> of the various +seasons of the year, demand particular attention and call for extra +observations at certain seasons: of these, three only have yet been +ascertained—the type for the middle of November—the annual depression +on or about the 28th of November—and the annual elevation on or about +the 25th of December. The enunciation of the first is as under: "That +during fourteen days in November, more or less equally disposed about +the middle of the month, the oscillations of the barometer exhibit a +remarkably symmetrical character, that is to say, the fall succeeding +the transit of the maximum or the highest reading is to a great extent +similar to the preceding rise. This rise and fall is not continuous or +unbroken; in some cases it consists of <i>five</i>, in others of <i>three</i> +distinct elevations. The complete rise and fall has been termed the +great symmetrical barometric wave of November. At its setting in the +barometer is generally low, sometimes below twenty-nine inches. This +depression is generally succeeded by <i>two</i> well-marked undulations, +varying from one to two days in<span class='pagenum'><a name="Page_49" id="Page_49">[Pg 49]</a></span> duration. The central undulation, which +also forms the apex of the great wave, is of larger extent, occupying +from three to five days; when this has passed, two smaller undulations +corresponding to those at the commencement of the wave make their +appearance, and at the close of the last the wave terminates." With but +slight exceptions, the observations of eight successive years have +confirmed the general correctness of this type. On two occasions the +central apex has not been the highest, and these deviations, with some +of a minor character, form the exceptions alluded to. This type only has +reference to London and the south-eastern parts of England; proceeding +westward, north-westward, and northward, the symmetrical character of +this type is considerably departed from; each locality possessing its +own type of the barometric movements during November. The desiderata in +immediate connexion with the November movements, as observed in the +southern and south-eastern parts of England, that present themselves, +are—the determination of the types for November, especially its middle +portion, as exhibited on the oceanic surface within an area comprised +between the 30th and 60th parallels, and the 1st and 40th meridians +west. Vessels sailing within this area may contribute greatly to the +determination of these types by making observations at intervals of +three hours from the 1st of November to the 7th or 8th of December. The +entire period of the great symmetrical wave of November will most +probably be embraced by such a series of observations, as well as the +annual depression of the 28th. For the elevation of the 25th of December +the three-hourly observations<span class='pagenum'><a name="Page_50" id="Page_50">[Pg 50]</a></span> should be commenced on the 21st, and +continued until the 3rd or 4th of the succeeding January.</p> + +<p>With respect to the great wave of November, our knowledge of it would be +much increased by such a series of observations as mentioned above, +being made on board surveying and other vessels employed off Scotland +and Ireland; vessels navigating the North Sea; vessels stationed off the +coasts of France, Spain, Portugal, and the northern parts of Africa, and +at all our stations in the Mediterranean. In this way the area of +examination would be greatly enlarged, and the <i>differences</i> of the +curves more fully elucidated; and this extended area of observation is +the more desirable, as there is some reason to believe that the line of +greatest symmetry <i>revolves</i> around a fixed point, most probably the +nodal point of the great European systems.</p> + +<p>It is highly probable that movements of a somewhat similar character, +although presenting very different curves, exist in the southern +hemisphere. The November wave is more or less associated with storms. It +has been generally preceded by a high barometer and succeeded by a low +one, and this low state of the barometer has been accompanied by stormy +weather. We are therefore prepared to seek for similar phænomena in the +southern hemisphere, in those localities which present similar states of +weather, and at seasons when such weather predominates. We have already +marked out the two capes in the Southern hemisphere for three-hourly +observations: they must doubtless possess very peculiar barometric +characters, stretching as they do into the vast area of the Southern +Ocean. It is highly probable that<span class='pagenum'><a name="Page_51" id="Page_51">[Pg 51]</a></span> the oscillations, especially at some +seasons, are very considerable, and vessels visiting them at such +seasons would do well to record with especial care the indications of +the instruments already alluded to. At present we know but little of the +barometric movements in the Southern hemisphere, and every addition to +our knowledge in this respect will open the way to more important +conclusions.</p> + +<p>It has been observed in the south-east of England that the barometer has +generally passed a maximum on or about the 3rd of every month, and this +has been so frequently the case as to form the rule rather than the +exception. The same fact during a more limited period has been observed +at Toronto. With especial reference to this subject the three-hourly +series of observations may be resorted to in all localities, but +especially north of the 40th parallel in the northern hemisphere. They +should be commenced at midnight immediately preceding the 1st and +continued to midnight succeeding the 5th.<span class='pagenum'><a name="Page_52" id="Page_52">[Pg 52]</a></span></p> + + + +<hr style="width: 65%;" /> +<h2>CHAPTER IV.</h2> + +<h3><span class="smcap">Practical Directions for Avoiding the Centres of Rotating +Storms.</span></h3> + + +<p>Figures 1 and 2, enlarged and printed on narrow rings of stiff +cardboard, are employed for this purpose. The letters outside the thick +circle are intended to distinguish the points of the compass, and in use +should always coincide with those points on the chart. The letters +within the thick circle indicate the direction of the wind in a +hurricane, the whirl being shown by the arrows between the letters. In +the northern hemisphere the direction of the whirl is always contrary to +that in which the hands of a watch move, and in the southern coincident +thereto. The graduation is intended to assist the mariner in +ascertaining the bearing of the centre of a storm from his ship.</p> + + +<p class='center'><i>Use.</i></p> + +<p>At any time when a severe gale or hurricane is expected, the seaman +should at once find the position of his ship on the chart, and place +upon it the graduated point which answers to the direction of the wind +at the time, taking care that the needle is directed to the north, so +that the exterior letters may point on the chart to the respective +points of the compass: this is very essential. This simple process will +at once acquaint the seaman with two important facts relative to the +coming hurricane<span class='pagenum'><a name="Page_53" id="Page_53">[Pg 53]</a></span>—his position in the storm, and the direction in +which it is moving.</p> + + +<p class='center'><i>Examples.</i></p> + +<p>A captain of a ship in latitude 35° 24' N., longitude 64° 12' W., bound +to the United States, observes the barometer to stand unusually high, +say 30·55 inches: shortly after the mercury begins to fall, at first +slowly and steadily; as the glass falls the wind freshens, and is +noticed to blow with increasing force from the S. so as to threaten a +gale. The position of the ship on the chart is now to be found, and the +graduated point under the letters <b>E.</b> S. is to be placed thereon, +taking care to direct the needle to the north. From these two +circumstances, the falling barometer and the wind blowing from the south +with increasing force, the mariner is aware of this simple fact, that he +is situated in the advancing portion of a body of air which is +proceeding towards the N.E.; and if he turn his face to the N.E. he will +find he is on the right of the axis line, or line cutting the advancing +body transversely. The hurricane circle as it lies on the chart reveals +to him another important fact, which is, that if he pursue his course he +will sail <i>towards</i> the axis line of the hurricane, and may stand a +chance of foundering in its centre. To avoid this he has one of two +courses to adopt; either to lay-to on the <i>starboard tack</i>, according to +Col. Reid's rules (see his 'Law of Storms,' 1st edit., pp. 425 to 428), +the ship being in the right-hand semicircle of the hurricane, or so to +alter his course as to keep without the influence of the storm. In the +present case the adoption of the latter alternative would involve<span class='pagenum'><a name="Page_54" id="Page_54">[Pg 54]</a></span> a +reversal of his former course; nevertheless it is clear the more he +bears to the S.E. the less he will experience the violence of the +hurricane: should he heave his ship to, upon moving the hurricane circle +from the ship's place on the chart towards the N.E., he will be able to +judge of the changes of the wind he is likely to experience: thus it +will first veer to S.S.W., the barometer still falling; then to S.W., +the barometer at a minimum—this marks the position of the most violent +portion of the storm he may be in, and by keeping the barometer as high +as he can by bearing towards the S.E., the farther he will be from the +centre—the barometer now begins to rise, the wind veering to W.S.W., +and the hurricane finally passes off with the wind at W. It is to be +particularly remarked that in this example the ship is in the <i>most +dangerous quadrant</i>, as by scudding she would be driven in advance of +the track of the storm's centre, which of course would be approaching +her.</p> + +<p>Assuming that the hurricane sets in at the ship's place with the wind at +S.E., the proceeding will be altogether different. At first the wind is +fair for the prosecution of the voyage, and it is desirable to take +advantage of this fair wind to avoid as much as possible the track of +the centre, which passes over the ship's place in this instance, and is +always the most dangerous part of the storm. As the ship is able to make +good distance from this track by bearing towards the N.W., provided she +has plenty of sea-room, she will experience less of the violence of the +hurricane; but as most of the Atlantic storms sweep over the shore, it +will be desirable to lay-to at some point on the <i>larboard tack</i>, the +ship being now in the left-hand<span class='pagenum'><a name="Page_55" id="Page_55">[Pg 55]</a></span> semicircle. By moving the circle as +before directed it will be seen that the veering of the wind is now +E.S.E., E., E.N.E., N.E., the lowest barometer N.N.E., N., and N.N.W., +the ship experiencing more or less of these changes as it is nearer to +or farther from the axis line.</p> + +<p>In latitudes lower than 20° N. the Atlantic hurricanes usually move +towards the N.W. Taking the same positions of our ship with regard to +the storms as in the two former examples, if the storm set in with the +wind E. the proper proceeding is to bear away for the N.E., the most +dangerous quadrant of the hurricane having overtaken the ship, the +veering of the wind if she is lying-to will be E., E.S.E., S.E., with +the lowest barometer S.S.E. and S. Should the storm set in at N.E., her +position at the time will be some indication of the distance of the +centre's track from the nearest land, and will greatly assist in +determining the point at which the captain ought to lay-to after taking +advantage of the N.E. wind, should he be able so to do, to bear away +from the centre line, so as to avoid as much as possible the violence of +the storm. From the proximity of the West Indian Islands to this +locality of the storm-paths, the danger is proportionally increased.</p> + +<p>The above examples have reference only to the lower and upper branches +of the storm paths of the Northern Atlantic in the neighbourhood of the +West Indies and the United States. In latitudes from about 25° to 32° +these paths usually <i>re-curve</i>, and at some point will move towards the +north. The veering of the wind will consequently be more or less +complicated according as the ship may be nearer to or farther from the +centre. The<span class='pagenum'><a name="Page_56" id="Page_56">[Pg 56]</a></span> tables on page 11, combined with the first of those +immediately following the next paragraph, will, it is hoped, prove +advantageous in assisting the mariner as to the course to be adopted. As +a general principle we should say it would be best to bear to the +eastward, so as not only to avoid the greater fury of the storm, but to +get into the S. and S.W. winds, which give the principal chances of +making a westerly course.</p> + +<p>We have in page 44 called attention to the fact that the storm paths +traced by Mr. Redfield do not extend eastward of the 50th meridian. This +by no means precludes the existence of severe storms and those of a +rotatory character in the great basin of the Northern Atlantic, +especially between the 40th and 50th parallels. A remarkable instance +has come under the author's attention of the wind hauling <i>apparently</i> +contrary to the usual theory: it may be that the storm route was in a +direction not generally observed. We are at the present moment destitute +of any information that at all indicates a <i>reversion</i> of the rotation +in either hemisphere. The following tables constructed for the northern +hemisphere, and for storm routes <i>not yet ascertained</i>, may probably be +consulted with advantage on anomalous occasions.</p> + + +<h4>HURRICANE MOVING FROM SOUTH TO NORTH.</h4> + +<p> +<span style="margin-left: 1em;">Axis line, wind E., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Axis line, wind W., barometer rising, last half of storm.</span><br /> +</p> + + +<h4>RIGHT-HAND SEMICIRCLE.</h4> + +<p> +<span style="margin-left: 1em;">Wind E.S.E., S.E., S.S.E., S., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Wind W.S.W., S.W., S.S.W., S., barometer rising, last half of storm.</span><br /> +<span class='pagenum'><a name="Page_57" id="Page_57">[Pg 57]</a></span></p> + +<h4>LEFT-HAND SEMICIRCLE.</h4> + +<p> +<span style="margin-left: 1em;">Wind E.N.E., N.E., N.N.E., N., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Wind W.N.W., N.W., N.N.W., N., barometer rising, last half of storm.</span><br /> +</p> + + +<h4>HURRICANE MOVING FROM NORTH TO SOUTH.</h4> + +<p> +<span style="margin-left: 1em;">Axis line, wind W., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Axis line, wind E., barometer rising, last half of storm.</span><br /> +</p> + + +<h4>RIGHT-HAND SEMICIRCLE.</h4> + +<p> +<span style="margin-left: 1em;">Wind W.N.W., N.W., N.N.W., N., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Wind E.N.E., N.E., N.N.E., N., barometer rising, last half of storm.</span><br /> +</p> + + +<h4>LEFT-HAND SEMICIRCLE.</h4> + +<p> +<span style="margin-left: 1em;">Wind W.S.W., S.W., S.S.W., S., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Wind E.S.E., S.E., S.S.E., S,, barometer rising, last half of storm.</span><br /> +</p> + + +<h4>HURRICANE MOVING PROM WEST TO EAST.</h4> + +<p> +<span style="margin-left: 1em;">Axis line, wind S., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Axis line, wind N., barometer rising, last half of storm.</span><br /> +</p> + + +<h4>RIGHT-HAND SEMICIRCLE.</h4> + +<p> +<span style="margin-left: 1em;">Wind S.S.W., S.W., W.S.W., W., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Wind N.N.W., N.W., W.N.W., W., barometer rising, last half of storm.</span><br /> +</p> + + +<h4>LEFT-HAND SEMICIRCLE.</h4> + +<p> +<span style="margin-left: 1em;">Wind S.S.E., S.E., E.S.E., E., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Wind N.N.E., N.E., E.N.E., E., barometer rising, last half of storm.</span><br /> +<span class='pagenum'><a name="Page_58" id="Page_58">[Pg 58]</a></span></p> + +<h4>HURRICANE MOVING FROM NORTH-WEST TO SOUTH-EAST.</h4> + +<p> +<span style="margin-left: 1em;">Axis line, wind S.W., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Axis line, wind N.E., barometer rising, last half of storm.</span><br /> +</p> + + +<h4>RIGHT-HAND SEMICIRCLE.</h4> + +<p> +<span style="margin-left: 1em;">Wind W.S.W., W., W.N.W., N.W., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Wind N.N.E., N., N.N.W., N.W., barometer rising, last half of storm.</span><br /> +</p> + + +<h4>LEFT-HAND SEMICIRCLE.</h4> + +<p> +<span style="margin-left: 1em;">Wind S.S.W., S., S.S.E., S.E., barometer falling, first half of storm.</span><br /> +<span style="margin-left: 1em;">Wind E.N.E., E., E.S.E., S.E., barometer rising, last half of storm.</span><br /> +</p> + + + +<hr style="width: 65%;" /> +<h2>APPENDIX.</h2> + +<h4>TABLE I.—Correction to be added to Barometers for Capillary Action.</h4> + +<p><br /><br /></p> + +<table border="1" cellpadding="4" width="65%" cellspacing="0" summary="Appendix Table 1"> +<tr> +<th rowspan="2">Diameter of Tube.</th> +<th colspan="2">Correction for</th> +</tr> +<tr> +<th>Unboiled Tubes.</th> +<th>Boiled Tubes.</th> +</tr> +<tr> +<td align="center">Inch.</td> +<td align="center">Inch.</td> +<td align="center">Inch.</td> +</tr> +<tr> +<td align="center">0·60</td> +<td align="center">0·004</td> +<td align="center">0·002</td> +</tr> +<tr> +<td align="center">0·50</td> +<td align="center">0·007</td> +<td align="center">0·003</td> +</tr> +<tr> +<td align="center">0·45</td> +<td align="center">0·010</td> +<td align="center">0·005</td> +</tr> +<tr> +<td align="center">0·40</td> +<td align="center">0·014</td> +<td align="center">0·007</td> +</tr> +<tr> +<td align="center">0·35</td> +<td align="center">0·020</td> +<td align="center">0·010</td> +</tr> +<tr> +<td align="center">0·30</td> +<td align="center">0·028</td> +<td align="center">0·014</td> +</tr> +<tr> +<td align="center">0·25</td> +<td align="center">0·040</td> +<td align="center">0·020</td> +</tr> +<tr> +<td align="center">0·20</td> +<td align="center">0·060</td> +<td align="center">0·029</td> +</tr> +<tr> +<td align="center">0·15</td> +<td align="center">0·088</td> +<td align="center">0·044</td> +</tr> +<tr> +<td align="center">0·10</td> +<td align="center">0·142</td> +<td align="center">0·070</td> +</tr> +</table> + +<p><span class='pagenum'><a name="Page_59" id="Page_59">[Pg 59]</a></span></p> +<p><br /><br /></p> +<p>TABLE II.—Correction to be applied to Barometers with <i>Brass Scales</i>, +extending from the Cistern to the top of the Mercurial Column, to reduce +the observation to 32° Fahrenheit.</p> + + +<p><br /></p> + +<table border="1" cellpadding="4" width="100%" cellspacing="0" summary="Appendix Table 2"> +<tr><th>T</th><th colspan="15" rowspan="3">INCHES.</th><th>T</th></tr> +<tr> +<th>e</th> +<th>e</th> +</tr> +<tr> +<th>m</th> +<th>m</th> +</tr> +<tr> +<th>p.</th> +<td>24</td> +<td align="center">24·5</td> +<td align="center">25</td> +<td align="center">25·5</td> +<td align="center">26</td> +<td align="center">26·5</td> +<td align="center">27</td> +<td align="center">27·5</td> +<td align="center">28</td> +<td align="center">28·5</td> +<td align="center">29</td> +<td align="center">29·5</td> +<td align="center">30</td> +<td align="center">30·5</td> +<td align="center">31</td> +<th>p.</th> +</tr> +<tr> +<td align="center">°</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +<td align="center">+</td> +</tr> +<tr> +<td align="center">0</td> +<td align="center">·061</td> +<td align="center">·063</td> +<td align="center">·064</td> +<td align="center">·065</td> +<td align="center">·067</td> +<td align="center">·068</td> +<td align="center">·069</td> +<td align="center">·071</td> +<td align="center">·072</td> +<td align="center">·073</td> +<td align="center">·074</td> +<td align="center">·076</td> +<td align="center">·077</td> +<td align="center">·078</td> +<td align="center">·080</td> +<td align="center">0</td> +</tr> +<tr> +<td align="center">1</td> +<td align="center">·059</td> +<td align="center">·061</td> +<td align="center">·062</td> +<td align="center">·063</td> +<td align="center">·064</td> +<td align="center">·064</td> +<td align="center">·065</td> +<td align="center">·067</td> +<td align="center">·069</td> +<td align="center">·071</td> +<td align="center">·072</td> +<td align="center">·073</td> +<td align="center">·074</td> +<td align="center">·076</td> +<td align="center">·077</td> +<td align="center">1</td> +</tr> +<tr> +<td align="center">2</td> +<td align="center">·057</td> +<td align="center">·058</td> +<td align="center">·060</td> +<td align="center">·061</td> +<td align="center">·062</td> +<td align="center">·063</td> +<td align="center">·064</td> +<td align="center">·066</td> +<td align="center">·067</td> +<td align="center">·068</td> +<td align="center">·069</td> +<td align="center">·070</td> +<td align="center">·072</td> +<td align="center">·073</td> +<td align="center">·074</td> +<td align="center">2</td> +</tr> +<tr> +<td align="center">3</td> +<td align="center">·055</td> +<td align="center">·056</td> +<td align="center">·057</td> +<td align="center">·059</td> +<td align="center">·060</td> +<td align="center">·061</td> +<td align="center">·062</td> +<td align="center">·063</td> +<td align="center">·064</td> +<td align="center">·065</td> +<td align="center">·067</td> +<td align="center">·068</td> +<td align="center">·069</td> +<td align="center">·070</td> +<td align="center">·071</td> +<td align="center">3</td> +</tr> +<tr> +<td align="center">4</td> +<td align="center">·053</td> +<td align="center">·054</td> +<td align="center">·055</td> +<td align="center">·056</td> +<td align="center">·057</td> +<td align="center">·058</td> +<td align="center">·059</td> +<td align="center">·061</td> +<td align="center">·062</td> +<td align="center">·063</td> +<td align="center">·064</td> +<td align="center">·065</td> +<td align="center">·066</td> +<td align="center">·067</td> +<td align="center">·068</td> +<td align="center">4</td> +</tr> +<tr> +<td align="center">5</td> +<td align="center">·051</td> +<td align="center">·052</td> +<td align="center">·053</td> +<td align="center">·054</td> +<td align="center">·055</td> +<td align="center">·056</td> +<td align="center">·057</td> +<td align="center">·058</td> +<td align="center">·059</td> +<td align="center">·060</td> +<td align="center">·061</td> +<td align="center">·062</td> +<td align="center">·063</td> +<td align="center">·065</td> +<td align="center">·066</td> +<td align="center">5</td> +</tr> +<tr> +<td align="center">6</td> +<td align="center">·049</td> +<td align="center">·050</td> +<td align="center">·051</td> +<td align="center">·052</td> +<td align="center">·053</td> +<td align="center">·054</td> +<td align="center">·055</td> +<td align="center">·056</td> +<td align="center">·057</td> +<td align="center">·058</td> +<td align="center">·059</td> +<td align="center">·060</td> +<td align="center">·061</td> +<td align="center">·062</td> +<td align="center">·063</td> +<td align="center">6</td> +</tr> +<tr> +<td align="center">7</td> +<td align="center">·046</td> +<td align="center">·047</td> +<td align="center">·048</td> +<td align="center">·049</td> +<td align="center">·050</td> +<td align="center">·051</td> +<td align="center">·052</td> +<td align="center">·053</td> +<td align="center">·054</td> +<td align="center">·055</td> +<td align="center">·056</td> +<td align="center">·057</td> +<td align="center">·058</td> +<td align="center">·059</td> +<td align="center">·060</td> +<td align="center">7</td> +</tr> +<tr> +<td align="center">8</td> +<td align="center">·044</td> +<td align="center">·045</td> +<td align="center">·046</td> +<td align="center">·047</td> +<td align="center">·048</td> +<td align="center">·049</td> +<td align="center">·050</td> +<td align="center">·051</td> +<td align="center">·052</td> +<td align="center">·053</td> +<td align="center">·054</td> +<td align="center">·054</td> +<td align="center">·055</td> +<td align="center">·056</td> +<td align="center">·057</td> +<td align="center">8</td> +</tr> +<tr> +<td align="center">9</td> +<td align="center">·042</td> +<td align="center">·043</td> +<td align="center">·044</td> +<td align="center">·045</td> +<td align="center">·046</td> +<td align="center">·046</td> +<td align="center">·047</td> +<td align="center">·048</td> +<td align="center">·049</td> +<td align="center">·050</td> +<td align="center">·051</td> +<td align="center">·052</td> +<td align="center">·053</td> +<td align="center">·054</td> +<td align="center">·054</td> +<td align="center">9</td> +</tr> +<tr> +<td align="center">10</td> +<td align="center">·040</td> +<td align="center">·041</td> +<td align="center">·042</td> +<td align="center">·042</td> +<td align="center">·043</td> +<td align="center">·044</td> +<td align="center">·045</td> +<td align="center">·046</td> +<td align="center">·047</td> +<td align="center">·047</td> +<td align="center">·048</td> +<td align="center">·049</td> +<td align="center">·050</td> +<td align="center">·051</td> +<td align="center">·052</td> +<td align="center">10</td> +</tr> +<tr><th colspan="17"> </th></tr> +<tr> +<td align="center">11</td> +<td align="center">·038</td> +<td align="center">·039</td> +<td align="center">·039</td> +<td align="center">·040</td> +<td align="center">·041</td> +<td align="center">·042</td> +<td align="center">·042</td> +<td align="center">·043</td> +<td align="center">·044</td> +<td align="center">·045</td> +<td align="center">·046</td> +<td align="center">·046</td> +<td align="center">·047</td> +<td align="center">·048</td> +<td align="center">·049</td> +<td align="center">11</td> +</tr> +<tr> +<td align="center">12</td> +<td align="center">·036</td> +<td align="center">·036</td> +<td align="center">·037</td> +<td align="center">·038</td> +<td align="center">·039</td> +<td align="center">·039</td> +<td align="center">·040</td> +<td align="center">·041</td> +<td align="center">·042</td> +<td align="center">·042</td> +<td align="center">·043</td> +<td align="center">·044</td> +<td align="center">·045</td> +<td align="center">·045</td> +<td align="center">·046</td> +<td align="center">12</td> +</tr> +<tr> +<td align="center">13</td> +<td align="center">·033</td> +<td align="center">·034</td> +<td align="center">·035</td> +<td align="center">·036</td> +<td align="center">·036</td> +<td align="center">·037</td> +<td align="center">·038</td> +<td align="center">·038</td> +<td align="center">·039</td> +<td align="center">·040</td> +<td align="center">·040</td> +<td align="center">·041</td> +<td align="center">·042</td> +<td align="center">·043</td> +<td align="center">·043</td> +<td align="center">13</td> +</tr> +<tr> +<td align="center">14</td> +<td align="center">·031</td> +<td align="center">·032</td> +<td align="center">·033</td> +<td align="center">·033</td> +<td align="center">·034</td> +<td align="center">·035</td> +<td align="center">·035</td> +<td align="center">·036</td> +<td align="center">·037</td> +<td align="center">·037</td> +<td align="center">·038</td> +<td align="center">·038</td> +<td align="center">·039</td> +<td align="center">·040</td> +<td align="center">·040</td> +<td align="center">14</td> +</tr> +<tr> +<td align="center">15</td> +<td align="center">·029</td> +<td align="center">·030</td> +<td align="center">·030</td> +<td align="center">·031</td> +<td align="center">·032</td> +<td align="center">·032</td> +<td align="center">·033</td> +<td align="center">·033</td> +<td align="center">·034</td> +<td align="center">·035</td> +<td align="center">·035</td> +<td align="center">·036</td> +<td align="center">·036</td> +<td align="center">·037</td> +<td align="center">·038</td> +<td align="center">15</td> +</tr> +<tr> +<td align="center">16</td> +<td align="center">·027</td> +<td align="center">·028</td> +<td align="center">·028</td> +<td align="center">·029</td> +<td align="center">·029</td> +<td align="center">·030</td> +<td align="center">·030</td> +<td align="center">·031</td> +<td align="center">·032</td> +<td align="center">·032</td> +<td align="center">·033</td> +<td align="center">·033</td> +<td align="center">·034</td> +<td align="center">·034</td> +<td align="center">·035</td> +<td align="center">16</td> +</tr> +<tr> +<td align="center">17</td> +<td align="center">·025</td> +<td align="center">·025</td> +<td align="center">·026</td> +<td align="center">·026</td> +<td align="center">·027</td> +<td align="center">·027</td> +<td align="center">·028</td> +<td align="center">·028</td> +<td align="center">·029</td> +<td align="center">·030</td> +<td align="center">·030</td> +<td align="center">·031</td> +<td align="center">·031</td> +<td align="center">·032</td> +<td align="center">·032</td> +<td align="center">17</td> +</tr> +<tr> +<td align="center">18</td> +<td align="center">·023</td> +<td align="center">·023</td> +<td align="center">·024</td> +<td align="center">·024</td> +<td align="center">·025</td> +<td align="center">·025</td> +<td align="center">·025</td> +<td align="center">·026</td> +<td align="center">·026</td> +<td align="center">·027</td> +<td align="center">·027</td> +<td align="center">·028</td> +<td align="center">·028</td> +<td align="center">·029</td> +<td align="center">·029</td> +<td align="center">18</td> +</tr> +<tr> +<td align="center">19</td> +<td align="center">·021</td> +<td align="center">·021</td> +<td align="center">·021</td> +<td align="center">·022</td> +<td align="center">·022</td> +<td align="center">·023</td> +<td align="center">·023</td> +<td align="center">·024</td> +<td align="center">·024</td> +<td align="center">·024</td> +<td align="center">·025</td> +<td align="center">·025</td> +<td align="center">·026</td> +<td align="center">·026</td> +<td align="center">·027</td> +<td align="center">19</td> +</tr> +<tr> +<td align="center">20</td> +<td align="center">·018</td> +<td align="center">·019</td> +<td align="center">·019</td> +<td align="center">·020</td> +<td align="center">·020</td> +<td align="center">·020</td> +<td align="center">·021</td> +<td align="center">·021</td> +<td align="center">·021</td> +<td align="center">·022</td> +<td align="center">·022</td> +<td align="center">·023</td> +<td align="center">·023</td> +<td align="center">·023</td> +<td align="center">·024</td> +<td align="center">20</td> +</tr> +<tr><th colspan="17"> </th></tr> +<tr> +<td align="center">21</td> +<td align="center">·016</td> +<td align="center">·017</td> +<td align="center">·017</td> +<td align="center">·017</td> +<td align="center">·018</td> +<td align="center">·018</td> +<td align="center">·018</td> +<td align="center">·019</td> +<td align="center">·019</td> +<td align="center">·019</td> +<td align="center">·020</td> +<td align="center">·020</td> +<td align="center">·020</td> +<td align="center">·021</td> +<td align="center">·021</td> +<td align="center">21</td> +</tr> +<tr> +<td align="center">22</td> +<td align="center">·014</td> +<td align="center">·014</td> +<td align="center">·015</td> +<td align="center">·015</td> +<td align="center">·015</td> +<td align="center">·016</td> +<td align="center">·016</td> +<td align="center">·016</td> +<td align="center">·016</td> +<td align="center">·017</td> +<td align="center">·017</td> +<td align="center">·017</td> +<td align="center">·018</td> +<td align="center">·018</td> +<td align="center">·018</td> +<td align="center">22</td> +</tr> +<tr> +<td align="center">23</td> +<td align="center">·012</td> +<td align="center">·012</td> +<td align="center">·012</td> +<td align="center">·013</td> +<td align="center">·013</td> +<td align="center">·013</td> +<td align="center">·013</td> +<td align="center">·014</td> +<td align="center">·014</td> +<td align="center">·014</td> +<td align="center">·014</td> +<td align="center">·015</td> +<td align="center">·015</td> +<td align="center">·015</td> +<td align="center">·015</td> +<td align="center">23</td> +</tr> +<tr> +<td align="center">24</td> +<td align="center">·010</td> +<td align="center">·010</td> +<td align="center">·010</td> +<td align="center">·010</td> +<td align="center">·011</td> +<td align="center">·011</td> +<td align="center">·011</td> +<td align="center">·011</td> +<td align="center">·011</td> +<td align="center">·012</td> +<td align="center">·012</td> +<td align="center">·012</td> +<td align="center">·012</td> +<td align="center">·012</td> +<td align="center">·013</td> +<td align="center">24</td> +</tr> +<tr> +<td align="center">25</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·010</td> +<td align="center">·010</td> +<td align="center">25</td> +</tr> +<tr> +<td align="center">26</td> +<td align="center">·005</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·007</td> +<td align="center">·007</td> +<td align="center">·007</td> +<td align="center">·007</td> +<td align="center">·007</td> +<td align="center">26</td> +</tr> +<tr> +<td align="center">27</td> +<td align="center">·003</td> +<td align="center">·003</td> +<td align="center">·003</td> +<td align="center">·003</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">27</td> +</tr> +<tr> +<td align="center">28</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">28</td> +</tr> +<tr> +<td align="center"> </td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center">—</td> +<td align="center"> </td> +</tr> +<tr> +<td align="center">29</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">·001</td> +<td align="center">29</td> +</tr> +<tr> +<td align="center">30</td> +<td align="center">·003</td> +<td align="center">·003</td> +<td align="center">·003</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">·004</td> +<td align="center">30</td> +</tr> +<tr><th colspan="17"> </th></tr> +<tr> +<td align="center">31</td> +<td align="center">·005</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·006</td> +<td align="center">·007</td> +<td align="center">·007</td> +<td align="center">·007</td> +<td align="center">·007</td> +<td align="center">·007</td> +<td align="center">31</td> +</tr> +<tr> +<td align="center">32</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·008</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·009</td> +<td align="center">·010</td> +<td align="center">·010</td> +<td align="center">32</td> +</tr> +<tr> +<td align="center">33</td> +<td align="center">·010</td> +<td align="center">·010</td> +<td align="center">·010</td> +<td align="center">·010</td> +<td align="center">·011</td> +<td align="center">·011</td> +<td align="center">·011</td> +<td 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align="center">·162</td> +<td align="center">·165</td> +<td align="center">·168</td> +<td align="center">·171</td> +<td align="center">·174</td> +<td align="center">·178</td> +<td align="center">·180</td> +<td align="center">·183</td> +<td align="center">·186</td> +<td align="center">·189</td> +<td align="center">97</td> +</tr> +<tr> +<td align="center">98</td> +<td align="center">·148</td> +<td align="center">·152</td> +<td align="center">·155</td> +<td align="center">·158</td> +<td align="center">·161</td> +<td align="center">·164</td> +<td align="center">·167</td> +<td align="center">·170</td> +<td align="center">·173</td> +<td align="center">·176</td> +<td align="center">·179</td> +<td align="center">·183</td> +<td align="center">·186</td> +<td align="center">·188</td> +<td align="center">·191</td> +<td align="center">98</td> +</tr> +<tr> +<td align="center">99</td> +<td align="center">·151</td> +<td align="center">·154</td> +<td align="center">·157</td> +<td align="center">·160</td> +<td align="center">·163</td> +<td align="center">·166</td> +<td align="center">·169</td> +<td align="center">·173</td> +<td align="center">·176</td> +<td align="center">·179</td> +<td align="center">·182</td> +<td align="center">·185</td> +<td align="center">·188</td> +<td align="center">·191</td> +<td align="center">·194</td> +<td align="center">99</td> +</tr> +<tr> +<td align="center">100</td> +<td align="center">·153</td> +<td align="center">·156</td> +<td align="center">·159</td> +<td align="center">·162</td> +<td align="center">·165</td> +<td align="center">·169</td> +<td align="center">·172</td> +<td align="center">·175</td> +<td align="center">·178</td> +<td align="center">·181</td> +<td align="center">·184</td> +<td align="center">·188</td> +<td align="center">·191</td> +<td align="center">·194</td> +<td align="center">·197</td> +<td align="center">100</td> +</tr> +</table> + + + + +<p><span class='pagenum'><a name="Page_60" id="Page_60">[Pg 60]</a></span></p> + +<p><br /><br /></p> + +<h2>FOOTNOTES</h2> +<div class="footnotes"> +<div class="footnote"><p><a name="Footnote_1_1" id="Footnote_1_1"></a><a href="#FNanchor_1_1"><span class="label">[1]</span></a> The first half of the storm, <i>in the case before alluded +to</i>, is that N.E. of the line N.W.—S.E., fig. 1, comprising the +easterly and southerly winds; and the latter half, that S.W. of the same +line, comprising the northerly and westerly winds.</p></div> + +<div class="footnote"><p><a name="Footnote_2_2" id="Footnote_2_2"></a><a href="#FNanchor_2_2"><span class="label">[2]</span></a> This table is also applicable to the hurricanes in the +neighbourhood of Mauritius in the southern hemisphere, where all the +phænomena are reversed; the motion of the hurricanes being towards the +S.W., and the rotation in the direction of the hands of a watch, the +same barometric and anemonal phænomena are experienced as in a hurricane +in the northern hemisphere moving towards the N.E.</p></div> + +<div class="footnote"><p><a name="Footnote_3_3" id="Footnote_3_3"></a><a href="#FNanchor_3_3"><span class="label">[3]</span></a> By the officer of the watch being charged with this duty, +and its being executed under his immediate superintendence, it is +apprehended that a register may be kept with great regularity.</p></div> + +<div class="footnote"><p><a name="Footnote_4_4" id="Footnote_4_4"></a><a href="#FNanchor_4_4"><span class="label">[4]</span></a> These papers may be obtained from Messrs. W. H. Allen and +Co., Booksellers to the Honourable East India Company, No. 7, Leadenhall +Street, London.</p></div> + +<div class="footnote"><p><a name="Footnote_5_5" id="Footnote_5_5"></a><a href="#FNanchor_5_5"><span class="label">[5]</span></a> Reports of the British Association for the Advancement of +Science, 1846, p. 139.</p></div></div> +<p><br /><br /></p> + +<p class='center'>PRINTED BY W. CLOWES AND SONS, STANFORD STREET.</p> + + + + + + + + + +<pre> + + + + + +End of Project Gutenberg's The Hurricane Guide, by William Radcliff Birt + +*** END OF THIS PROJECT GUTENBERG EBOOK THE HURRICANE GUIDE *** + +***** This file should be named 18534-h.htm or 18534-h.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/1/8/5/3/18534/ + +Produced by Carlos Traversi, Janet Blenkinship, and the +Online Distributed Proofreaders Europe at +http://dp.rastko.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Hurricane Guide + Being An Attempt To Connect The Rotary Gale Or Revolving + Storm With Atmospheric Waves. + +Author: William Radcliff Birt + +Release Date: June 8, 2006 [EBook #18534] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK THE HURRICANE GUIDE *** + + + + +Produced by Carlos Traversi, Janet Blenkinship, and the +Online Distributed Proofreaders Europe at +http://dp.rastko.net + + + + + + + + + + + THE + + HURRICANE GUIDE: + + + BEING + + AN ATTEMPT TO CONNECT THE + + ROTATORY GALE OR REVOLVING STORM + + WITH + + ATMOSPHERIC WAVES. + + INCLUDING INSTRUCTIONS FOR OBSERVING THE PHAENOMENA OF THE WAVES AND + STORMS; + + + WITH + + PRACTICAL DIRECTIONS FOR AVOIDING THE CENTRES OF THE LATTER. + + BY + + WILLIAM RADCLIFF BIRT. + + + LONDON: JOHN MURRAY, ALBEMARLE STREET. + _PUBLISHER TO THE ADMIRALTY._ + 1850. + + PRINTED BY W. CLOWES AND SONS, STAMFORD STREET. + + + + +PREFACE. + + +In introducing the following pages to the notice of the Public, it is +the Author's wish to exhibit in as clear a light as our present +researches on the subjects treated of will allow, the connexion between +one of the most terrific phaenomena with which our globe is visited, and +a phaenomenon which, although but little known, appears to be intimately +connected with revolving storms. How far he has succeeded, either in +this particular object or in endeavouring to render the essential +phaenomena of storms familiar to the seaman, is left for the Public to +determine. Should any advantage be found to result from the study of the +Atmospheric Waves, as explained and recommended in this little work, or +the seaman be induced by its perusal to attend more closely to the +observations of those instruments that are calculated to warn him of his +danger, an object will be attained strikingly illustrative of the +Baconian aphorism, "Knowledge is Power." + + _Bethnal Green_, April 19, 1849. + + + + + CONTENTS. + + + PAGE + + CHAP. I.--PHAENOMENA OF REVOLVING STORMS 7 + + " II.--PHAENOMENA OF ATMOSPHERIC WAVES 13 + + " III.--OBSERVATIONS 18 + + SECT. I.--Instruments 19 + + " II.--Times of Observation 28 + + " III.--Localities for Additional Observations 31 + + " IV.--Storms, Hurricanes, and Typhoons 43 + + " V.--Seasons for Extra Observations 48 + + " IV.--PRACTICAL DIRECTIONS FOR AVOIDING THE CENTRES + OF STORMS 52 + + + + +NOTICE. + + +In the pocket accompanying this work are two rings of stiff cardboard, +on which will be found all the information contained in figures 1 and 2. +When they are laid flatly upon a chart, the continuity of the lines on +the chart is not materially interfered with, while the idea of a body of +air rotating in the direction indicated by the arrows is conspicuously +presented to the mind. These rings are more particularly referred to on +page 52. + + + + +THE + +HURRICANE GUIDE. + + + + + +CHAPTER I. + +PHAENOMENA OF REVOLVING STORMS. + + +It is the object of the following pages to exhibit, so far as +observation may enable us, and in as brief a manner as possible, the +connexion, if any, that exists between those terrific meteorological +phaenomena known as "revolving storms," and those more extensive and +occult but not less important phaenomena, "atmospheric waves." + +To the great body of our seamen, whether in her Majesty's or the +mercantile service, the subject can present none other than the most +interesting features. The laws that govern the transmission of large +bodies of air from one part of the oceanic surface to another, either in +a state of rapid rotation or presenting a more or less rectilineal +direction, must at all times form an important matter of inquiry, and +bear very materially on the successful prosecution of the occupation of +the voyager. + +In order to place the subjects above alluded to in such a point of view +that the connexion between them may be readily seen, it will be +important to notice the principal phaenomena presented by each. Without +going over the ground so well occupied by those able writers on the +subject of storms--Redfield, Reid, Piddington, and Thom--it will be +quite sufficient for our present purpose simply to notice the essential +phaenomena of revolving storms as manifested by the barometer and vane. +The usual indications of a storm in connexion with these instruments are +the _falling_ of the barometer and the _freshening_ of the wind, and it +is generally considered that a _rapid_ fall of the mercury in the +hurricane regions invariably precedes the setting in of a storm. + +There are three classes of phaenomena that present themselves to an +observer, according as he is situated _on_ the line or axis of +translation, or _in_ either the right or left hand semicircle of the +storm. These will be rendered very apparent by a little attention to the +annexed engraving, fig. 1. + +[Illustration: Compass rose] + +In this figure the arrow-head is supposed to be directed true north, and +the hurricane--as is the case in the American storms north of the 30th +parallel--to be moving towards the N.E. on the line N.E.--S.W. If the +ship take the hurricane with the wind S.E.,--the letters within the two +larger circles indicating _the direction of the wind in the storm_ +according to the rotation as shown by the circle of arrow-heads, and +which it is to be particularly noted is in the northern hemisphere +_contrary to the direction in which the hands of a watch move_: in the +southern hemisphere the rotation is reversed--the only phaenomena +presented by the storm are as follows:--The wind continues to blow from +the S.E., increasing considerably in force with the barometer falling to +a very great extent until the centre of the storm reaches the ship, when +the fury of the winds is hushed, and a lull or calm takes place, +generally for about half an hour, after which the wind springs up mostly +with increased violence, but from the opposite quarter N.W., the +barometer begins to rise, and as the storm passes off, the force of the +wind abates. + +The point to which we wish particularly to direct attention in connexion +with this exposition of the phaenomena attending the transmission of a +storm is this:--If the observer so place himself at the commencement +that the wind passes _from his left hand towards his right_, his face +will be directed towards the centre of the storm; and the wind +undergoing no change in direction, but only in force, will acquaint him +with this important fact that the _centre_ is not only gradually but +surely approaching him: in other words, in the case before us, when he +finds the wind from the S.E., and he places himself with his face to the +S.W. he is looking towards the centre, and the wind rushes past him +_from his left to his right hand_. Now the connexion of the barometer +with this phase of the storm is _falling with the wind from left to +right, the observer facing the centre while the first half is +transiting_.[1] During the latter half these conditions are reversed, +the observer still keeping his position, his face directed to the S.W., +the barometer _rises_ with a N.W. wind, which rushes past him _from his +right to his left hand_ with a decreasing force. We have therefore _a +rising barometer with the wind from right to left during the latter half +of the storm, the observer having his back to the centre_. + +The above _general_ enunciations of the barometric and anemonal +phaenomena of a rotating storm hold good with regard to the _northern_ +hemisphere, whatever may be the direction in which the hurricanes +advance. This may be placed in a clearer light, as well as the remaining +classes of phaenomena shown, by consulting the following tables, +constructed for the basin of the Northern Atlantic, and comparing them +with fig. 1. In this basin, with lower latitudes than 25 deg., the usual +paths of the hurricanes are towards the north-west, in higher latitudes +than 30 deg. towards the north-east. The tables exhibit the veering of the +wind with the movements of the barometer, according as the ship is +situated in the right or left hand semicircle of the hurricane. It must +here be understood that the right and left hand semicircles are +determined by the observer so placing himself that his face is directed +towards the quarter to which the hurricane is advancing. + + +LOWER LATITUDES. + +NORTHERN HEMISPHERE. + + Axis line, wind N.E., barometer falling, first half of storm. + Axis line, wind S.W., barometer rising, last half of storm. + +RIGHT-HAND SEMICIRCLE. + + Wind E.N.E., E., E.S.E., S.E., barometer falling, storm increasing. + Wind S.S.W., S., S.S.E., S.E., barometer rising, storm passing off. + +LEFT-HAND SEMICIRCLE. + + Wind N.N.E., N., N.N.W., N.W., barometer falling, storm increasing. + Wind W.S.W., W., W.N.W., N.W., barometer rising, storm passing off. + + +HIGHER LATITUDES. + +NORTHERN HEMISPHERE.[2] + + Axis line, wind S.E., barometer falling, first half of storm. + Axis line, wind N.W., barometer rising, last half of storm. + +RIGHT-HAND SEMICIRCLE. + + Wind S.S.E., S., S.S.W., S.W., barometer falling, storm increasing. + Wind W.N.W., W., W.S.W., S.W., barometer rising, storm passing off. + +LEFT-HAND SEMICIRCLE. + + Wind E.S.E., E., E.N.E., N.E., barometer falling, storm increasing. + Wind N.N.W., N., N.N.E., N.E., barometer rising, storm passing off. + +N.B. The directions of the hurricane winds are so arranged as to show +the points of commencement and termination. Thus in the lower latitudes +a storm commencing at E.N.E. passes off at S.S.W. after the wind has +veered E., E.S.E., S.E., S.S.E., and S., being in the order of the +letters in the upper line and contrary to their order in the lower. One +commencing at E.S.E. passes off at S.S.E. right-hand semicircle. In the +higher latitudes a ship taking the storm at E.N.E. will be in the +left-hand semicircle, and the hurricane will pass off at N.N.E. These +changes are rendered very apparent by moving the hurricane circle in the +direction in which the storm is expected to proceed. + +Fig. 2 represents the whirl and hurricane winds in the south. + +[Illustration: Fig. 2] + + + + +CHAPTER II. + +PHAENOMENA OF ATMOSPHERIC WAVES. + + +Professor Dove of Berlin has suggested that in the temperate zones the +compensating currents of the atmosphere necessary to preserve its +equilibrium may be arranged as parallel currents on the _surface_, and +not superposed as in or near the torrid zone. His views may be thus +enunciated:--That in the parallels of central Europe the N.E. current +flowing towards the equator to feed the ascending column of heated air +is not compensated by a current in the upper regions of the atmosphere +flowing from the S.W. as in the border of the torrid zone, but there are +also S.W. currents on each side the N.E., which to the various countries +over which they pass appear as surface-winds, the winds in fact being +disposed in alternate beds or layers, S.W., N.E., as in fig. 3. + +[Illustration: Fig. 3.] + +The Professor also suggests that these parallel and oppositely directed +winds are shifting, _i. e._ they gradually change their position with a +lateral motion in the direction of the large arrow cutting them +transversely. + +In the course of the author's researches on atmospheric waves he had an +opportunity of testing the correctness of Professor Dove's suggestion, +and in addition ascertained that there existed another set of oppositely +directed winds at right angles to those supposed to exist by the +Professor. These currents were N.W. and S.E. with a lateral motion +towards the N.E. He also carefully discussed the barometric phaenomena +with relation to both these sets of currents, and arrived at the +following conclusions. The details will be found in the author's third +report, presented to the British Association for the Advancement of +Science (Reports, 1846, pp. 132 to 162). During the period under +examination the author found the barometer generally to rise with N.E. +and N.W. winds, and fall with S.W. and S.E. winds, and that the +phaenomena might be thus illustrated:--Let the strata _a a a' a', b' b' b +b_, fig. 3, represent two parallel aerial currents or winds, _a a a' a'_ +from S.W. or S.E., and _b' b' b b_ from N.E. or N.W. and conceive them +both to advance from the N.W. in the first instance and from the S.W. in +the second, in the direction of the large arrow. Now conceive the +barometer to commence rising just as the edge _b b_ passes any line of +country, and to continue rising until the edge _b' b'_ arrives at that +line, when the maximum is attained. It will be remarked that this rise +is coincident with a N.E. or N.W. wind. The wind now changes and the +barometer begins to fall, and continues falling until the edge _a a_ +coincides with the line of country on which _b b_ first impinged. +During this process we have all the phaenomena exhibited by an +atmospheric wave: when the edge _b b_ passes a line of country the +barometer is at a _minimum_, and this minimum has been termed the +_anterior trough_. During the period the stratum _b' b' b b_ transits, +the barometer rises, and this rise has been called the _anterior slope_. +When the conterminous edges of the strata _a' a' b' b'_ pass, a +barometric _maximum_ extends along the line of country formerly occupied +by the anterior trough, and this maximum has been designated the +_crest_. During the transit of the stratum _a' a' a a_ the barometer +_falls_, and this fall has been characterised as the _posterior slope_; +and when the edge _a a_ occupies the place of _b b_, the descent of the +mercurial column is completed, another _minimum_ extends in the +direction of the former, and this minimum has been termed the _posterior +trough_. + +It will be readily seen that the lateral passage of the N.W. and S.E. +currents towards the N.E. presents precisely the same barometric and +anemonal phaenomena as the rotatory storms when moving in the same +direction. If the observer, when the barometer is at a _maximum_ with a +N.W. wind, place himself in the same position with regard to the +laterally advancing current as he did with regard to the advancing +storm, _i. e._ with his face _towards_ the quarter from which it is +advancing--S.W., he will find that with a _falling barometer and S.E. +wind the current passes him from the left to the right hand_; but if at +a barometric _minimum_ he place himself in the same position with his +face directed to the quarter from which the N.W. current is advancing +laterally, also S.W., he will find that with a rising barometer _and +N.W. wind the current passes him from right to left_. Now the two +classes of phaenomena are identical, and it would not be difficult to +show that, had we an instance of a rotatory storm in the northern +hemisphere moving from N.W. to S.E., it would present precisely the same +phaenomena as to the direction of currents passing from left to right and +from right to left with falling and rising barometers, increase and +decrease in the force of the wind, &c., as the oppositely directed +aerial currents do which pass over western central Europe. + +In the absence of direct evidence of the production of a revolving storm +from the crossing of two large waves, as suggested by Sir John Herschel, +although it is not difficult to obtain such evidence, especially from +the surface of the ocean, the identity of the two classes of phaenomena +exhibited by the storms and waves as above explained amounts to a strong +presumption that there is a close connexion between them, and that a +more minute investigation of the phaenomena of atmospheric waves is +greatly calculated to throw considerable light on the laws that govern +the storm paths in both hemispheres. The localities in which these +atmospheric movements, the waves, have been hitherto studied, have been +confined to the northern and central parts of Europe--the west of +Ireland, Alten in the north of Europe, Lougan near the Sea of Azov, and +Geneva, being the angular points of the included area. It will be +remarked that the greatest portion of this area is _inland_, but there +is one important feature which the study of the barometer has brought to +light, and which is by no means devoid of significance, viz. that the +oscillations are much greater in the neighbourhood of _water_, and this +appears to indicate that the junction lines of land and water form by +far the most important portions of the globe in which to study both the +phaenomena of storms and waves. It is also very desirable that our +knowledge of these phaenomena should, with immediate reference to the +surface of the ocean, be increased, and in this respect captains and +masters of vessels may render essential service by observing and +recording the state of the barometer, and direction and force of the +wind, several times in the course of the day and night;[3] and when it +is considered that the immediate object in view is one in which the +mariner is personally interested, and one in which, it may be, his own +safety is concerned, it is hoped that the keeping of a meteorological +register having especial reference to the indications of the barometer, +and force and direction of the wind, will not be felt as irksome, but +rather will be found an interesting occupation, the instruments standing +in the place of faithful monitors, directing when and where to avoid +danger, and the record furnishing important data whereby the knowledge +of general laws may be arrived at, having an essential bearing on the +interests of the service at large. + + + + +CHAPTER III. + +OBSERVATIONS. + + +In sketching out a system of observation having especial reference to +atmospheric waves and rotatory storms, regard has been had--_first_, to +the instruments that should be used, the observations to be made with +them, the corrections to be applied to such observations, and the form +of registry most suitable for recording the results: _second_, to the +times of observation: _third_, to the more important localities that +should be submitted to additional observation: _fourth_, to peculiar +phaenomena requiring extraordinary observations for their elucidation: +and _fifth_, to particular seasons, when the instruments should be +watched with more than ordinary care. + +The more important objects of observation having especial reference to +atmospheric waves are those points which have been termed _crests_ and +_troughs_. These are simply the _highest_ and _lowest_ readings of the +barometer, usually designated _maxima_ and _minima_, and should for the +object in view receive particular attention. Whenever there is reason to +believe that the barometer is approaching either a _maximum_ or +_minimum_, additional observations should be resorted to, so as to +secure as nearly as possible _the precise time_ as reckoned at the ship, +with her position, of its occurrence, as well as the altitude of the +mercurial column at that time and place. By means of such observations +as these on board several ships scattered over the surfaces of our great +oceans, much valuable information may be accumulated of a character +capable of throwing considerable light on the _direction_ in which the +lines of barometric maxima and minima stretch, and also a tolerably +accurate notion may be formed of their progress, both as regards +direction and rate. In immediate connexion with such observations +particular attention should be paid to the direction of the wind +according to the season. + + +SECTION I.--INSTRUMENTS. + +_Description and Position of Instruments._--The principal instrument +requisite in these observations is the barometer, which should be of the +marine construction, and as nearly alike as possible to those furnished +to the Antarctic expedition which sailed under the command of Sir James +Clark Ross. These instruments were similar to the ordinary portable +barometers, and differed from them only in the mode of their suspension +and the necessary contraction of the tubes to prevent oscillation from +the motion of the ship. The barometer on shipboard should be suspended +on a gimbal frame, which ought not to swing too freely, but rather so as +to deaden oscillations by some degree of friction. To the upper portion +of the tube in this construction of instrument light is alike accessible +either in front or behind, and the vernier is furnished with a back and +front edge, both being in precisely the same plane, nearly embracing the +tube, and sliding up and down it by the motion of rack-work; by the +graduation of the scale and vernier the altitude of the mercury can be +read off to .002 inch. + +When the barometer is placed in the ship, its position should be as near +midships as possible, out of the reach of sunshine, but in a good light +for reading, and in a situation in which it will be but little liable to +sudden gusts of wind and changes of temperature. Great care should be +taken to ascertain the exact height of its cistern above the water-line, +and in order to facilitate night observations every possible arrangement +should be made for placing behind it a light screened by white paper. + +_Observations._--The first thing to be done is the reading off and +recording the temperature indicated by the thermometer that in this +construction of instrument dips into the mercury in the cistern. Sir +John Herschel has suggested that "the bulb of the thermometer should be +so situated as to afford the best chance of its indicating the exact +mean of the whole barometric column, that is to say, fifteen inches +above the cistern enclosed within the case of the barometer, nearly in +contact with its tube, and with a stem so long as to be read off at the +upper level." + +Previous to making an observation with the barometer the instrument +should be slightly tapped to free the mercury from any adhesion to the +glass; any violent oscillation should, however, be carefully avoided. +The vernier should then be adjusted to the upper surface of the mercury +in the tube; for this purpose its back and front edges should be made to +coincide, that is, the eye should be placed in exactly the same plane +which passes through the edges; they should then be brought carefully +down until they form a tangent with the curve produced by the convex +surface of the mercury and the light is _just_ excluded from between +them and the point of contact. It is desirable in making this adjustment +that the eye should be assisted by a magnifying-glass. The reading of +the scale should then be taken and entered in the column appropriated to +it in the proper form. If the instrument have no tubular or double-edged +index, the eye should be placed carefully at the level of the upper +surface of the mercury and the index of the vernier brought gently down +to the same level so as apparently just to touch the surface, great care +being taken that the eye index and surface of the mercury are all in the +same plane. + +Each observation of the barometer should be accompanied by an +observation of the direction of the wind, which should be noted in the +usual manner in which it is observed at sea. In connexion with the +_direction_ the _force_ of the wind should be recorded in accordance +with the following scale, contrived by Admiral Sir Francis Beaufort:-- + + 0. Calm + 1. Light air or just sufficient to give steerage way. + 2. Light breeze { or that in which a well- } 1 to 2 knots. + 3. Gentle breeze { conditioned man of war, } 3 to 4 knots. + 4. Moderate breeze { with all sail set, and } 5 to 6 knots. + { clean full, would go in } + { smooth water, from } + 5. Fresh breeze } { Royals, &c. + 6. Strong breeze } { Single-reefed top-sails + } { and top-gallant + } or that in which such a { sails. + 7. Moderate gale } ship could just carry in { Double-reefed + } chase full and by { topsails, jib, &c. + 8. Fresh gale } { Triple-reefed + } { topsails, &c. + 9. Strong gale } { Close-reefed top-sails + } { and courses. + + 10. Whole gale or that with which she could scarcely bear + close-reefed main topsail and reefed foresail. + 11. Storm or that which reduces her to storm staysails. + 12. Hurricane or that which no canvas could withstand. + +_Corrections._--As soon after the observations have been made as +circumstances will permit, the reading of the barometer should be +_corrected_ for the relation existing between the capacities of the tube +and cistern (if its construction be such as to require that correction), +and for the capillary action of the tube; and then _reduced_ to the +standard temperature of 32 deg. Fahr., and to the sea-level, if on +shipboard. For the first correction the _neutral point_ should be marked +upon each instrument. It is that particular height which, in its +construction, has been actually measured from the surface of the mercury +in the cistern, and indicated by the scale. In general the mercury will +stand either above or below the neutral point; if _above_, a portion of +the mercury must have left the cistern, and consequently must have +_lowered_ the surface in the cistern: in this case the altitude as +measured by the scale will be _too short--vice versa_, if below. The +relation of the capacities of the tube and cistern should be +experimentally ascertained, and marked upon the instrument by the maker. +Suppose the capacity to be 1/50, marked thus on the instrument, +"_Capacity 1/50:_" this indicates that for every inch of variation of +the mercury in the tube, that in the cistern will vary contrariwise +1/50th of an inch. When the mercury in the tube is _above_ the neutral +point, the difference between it and the neutral point is to be reduced +in the proportion expressed by the "capacity" (in the case supposed, +divided by 50), and the quotient _added_ to the observed height; if +_below, subtracted_ from it. In barometers furnished with a fiducial +point for adjusting the lower level, this correction is superfluous, and +must not be applied. + +The second correction required is for the capillary action of the tube, +the effect of which is always to depress the mercury in the tube by a +certain quantity inversely proportioned to the diameter of the tube. +This quantity should be experimentally determined during the +construction of the instrument, and its amount marked upon it by the +maker, and is always to be _added_ to the height of the mercurial +column, previously corrected as before. For the convenience of those who +may have barometers, the capillary action of which has not been +determined, a table of corrections for tubes of different diameters is +placed in the Appendix, Table I. + +The next correction, and in some respects the most important of all, is +that due to the temperature of the mercury in the barometer tube at the +time of observation, and to the expansion of the scale. Table II. of the +Appendix gives for every degree of the thermometer and every half-inch +of the barometer, the proper quantity to be added or subtracted for the +reduction of the observed height to the standard temperature of the +mercury at 32 deg. Fahr. + +After these the index correction should be applied. This is the amount +of difference between the particular instrument and the readings of the +Royal Society's flint-glass barometer when properly corrected, and is +generally known as the _zero_. It is impossible to pay too much +attention to the determination of this point. For this purpose, when +practicable, the instrument should be immediately compared with the +Royal Society's standard, and the difference of the readings of both +instruments, when corrected as above, carefully noted and preserved. +Where, however, this is impracticable, the comparison should be effected +by means either of some other standard previously so compared, or of an +intermediate portable barometer, the zero point of which has been _well +determined_. Suspend the portable barometer as near as convenient to the +ship's barometer, and after at least an hour's quiet exposure, take as +many readings of both instruments as may be necessary to reduce the +probable error of the mean of the differences below 0.001 inch. Under +these circumstances the mean difference of all the readings will be the +_relative_ zero or index error, whence, if that of the intermediate +barometer be known, that of the other may be found. As such comparisons +will always be made when the vessel is in port, sufficient time can be +allowed for making the requisite number of observations: hourly readings +would perhaps be best, and they would have the advantage of forming part +of the system when in operation, and might be accordingly used as such. + +It is not only desirable that the zero point of the barometer should be +well determined in the first instance; it should also be carefully +verified on every opportunity which presents itself; and in every +instance, previous to sailing, it should be re-compared with the +standard on shore by the intervention of a portable barometer, and no +opportunity should be lost of comparing it on the voyage by means of +such an intermediate instrument with the standard barometers at St. +Helena, the Cape of Good Hope, Bombay, Madras, Paramatta, Van Diemen's +Island, and with any other instruments likely to be referred to as +standards, or employed in research elsewhere. Any vessel having a +portable barometer on board, the zero of which has been well determined, +would do well, on touching at any of the ports above named, to take +comparative readings with the standards at those ports, and record the +differences between the standard, the portable, and the ship barometers. +By such means the zero of one standard may be transported over the whole +world, and those of others compared with it ascertained. To do so, +however, with perfect effect, will require that the utmost care should +be taken of the portable barometer; it should be guarded as much as +possible from all accident, and should be kept safely in the "portable" +state when not immediately used for comparison. To transport a +well-authenticated zero from place to place is by no means a point of +trifling importance. Neither should it be executed hurriedly nor +negligently. Some of the greatest questions in meteorology depend on its +due execution, and the objects for which these instructions have been +prepared will be greatly advanced by the zero points of all barometers +being referred to one common standard. Upon the arrival of the vessel in +England, at the termination of the voyage, the ship's barometer should +be again compared with the same standard with which it was compared +previous to sailing; and should any difference be found, it should be +most carefully recorded. + +The correction for the height of the cistern _above_ or _below_ the +water-line is _additive_ in the former case, _subtractive_ in the +latter. Its amount may be taken, nearly enough, by allowing 0.001 in. of +the barometer for each foot of difference of level. + +An example of the application of these several corrections is +subjoined:-- + + + | _Attached Therm_. 54 deg..3. |_Data for the correction of | + | | the Instrument_. | + +---------------------------------------+-------------------------------+ + |Barometer reading. 29.409 |Neutral point 30.123 | + |Corr. for capacity - .017 |Capacity 1/42 | + | |Capillary action + .032 | + +---------------------------------------| | + | 29.392 |Zero to Royal Society + .036 | + |Corr. for capillarity + .032 |Corr. for altitude above | + | | water-line + .004 | + +---------------------------------------| | + | 29.424 | | + |Corr. for temperature - .068 | | + +---------------------------------------| | + | 29.356 | | + |Corr. for zero and water-line + .040 | | + +---------------------------------------| | + |Aggregate = pressure at | | + | sea-level 29.396 | | + +---------------------------------------+-------------------------------+ + + +It would greatly facilitate the comparison of the barometric +observations by projecting them in curves when all the proper +corrections have been applied. This may be accomplished by a much +smaller expenditure of time than may at first be supposed. A paper of +engraved squares on which the observations of twelve days may be laid +down on double the natural scale, would be very suitable for the +purpose.[4] The projection of each day's observations would occupy but a +short time; and should circumstances on any occasion prevent the +execution of it, when the ship was becalmed or leisure otherwise +afforded, it would form an interesting and useful occupation, and serve +to beguile some of the tedium often experienced at such intervals. + +_Registers._--For the particular object in view the register need not be +very extensive. One kept in the annexed form will be amply sufficient. +It should, however, be borne in mind that none but _uncorrected_ +observations should find admission; in point of fact it should be +strictly a register of phaenomena as _observed_, and on no account +whatever should any entry be made from recollection, or any attempt made +to fill up a blank by the apparent course of the numbers before and +after. The headings of the columns will, it is hoped, be sufficiently +explicit. It is desirable in practice that the column for remarks should +embrace an entire page opposite the other entries, in order that +occasional observations, as well as several other circumstances +continually coming under review in the course of keeping a journal, may +find entry. + +METEOROLOGICAL REGISTER kept on board ______ during her voyage from + ______ to ______ by ______. + + +---------+----+------+-------+------+------------------+--------+----------+ + | | | | | | Wind. | | | + | | | | | Att. |-----------+------| | | + | Date. |Lat.| Long.| Barom.| Ther.| Direction.|Force.| Remarks| Observer.| + |---------|----|------|-------|------|-----------|------|--------|----------| + | |h. m.| | | | | | | | | + | | | | | | | | | | | + | | | | | | | | | | | + | | | | | | | | | | | + | | | | | | | | | | | + | | | | | | | | | | | + +---+-----+----+------+-------+------+-----------+------+--------+----------+ + +The only difference between the above form and one for the reception of +_corrected_ readings will be the dispensing with the column for the +attached thermometer, and placing under the word Barom. "corrected." + + +II.--TIMES OF OBSERVATION. + +There can be no question that the greatest amount of information, the +accuracy of the data supplied, and in fact every meteorological element +necessary to increase our knowledge of atmospheric waves, may be best +obtained by an uninterrupted series of _hourly_ observations made on +board vessels from their leaving England until their safe arrival again +at the close of their respective voyages; but from a variety of +circumstances--the nature of the service in which the vessels may be +employed, particular states of the weather, &c.--such a course of +unremitting labour cannot be expected; it is therefore necessary to fix +on some stated hours at which the instruments before particularized +should be regularly observed throughout the voyage, and their +indications faithfully recorded. The hours of 3 A.M., 9 A.M., 3 P.M., +and 9 P.M., are now so generally known as _meteorological hours_, that +nothing should justify a departure from them; and it is the more +essential that these hours should be adopted in the present inquiry, +because the series of observations made at intervals terminated by these +hours can the more readily be used in connexion with those made +contemporaneously on land, and will also serve to carry on +investigations previously instituted, and which have received +considerable illustration by means of observations at the regular +meteorological hours; we therefore recommend their general adoption in +all observations conducted at sea. + +It is intended in the sequel to call attention to particular parts of +the earth's surface where it is desirable that additional observations +should be made, in order to furnish data of a more accurate character, +and to mark more distinctly barometric changes than the four daily +readings are capable of effecting. The best means of accomplishing this +for the object in view appears to be the division of the interval of six +hours into two equal portions, and to make the necessary observations +eight times in the course of twenty-four hours. In the particular +localities to which allusion has been made we recommend the following as +the hours of observation:-- + +A.M. 3, 6, 9, noon. P.M. 3, 6, 9, midnight. + +In other localities besides those hereafter to be mentioned, when +opportunities serve, readings at these hours would greatly enhance the +value of the four daily readings. + +There are, however, portions of the surface of our planet, and probably +also phaenomena that occur in its atmosphere, which require still closer +attention than the eight daily readings. One such portion would appear +to exist off the western coast of Africa, and we recommend the adoption +of _hourly_ readings while sailing to the westward of this junction of +aqueous and terrestrial surface; more attention will be directed to this +point as we proceed. There are also phaenomena the localities of which +may be undetermined, and the times of their occurrence unknown, but so +important a relation do they bear to the subject of our inquiries, that +they demand the closest attention. They will be more particularly +described under the head of accumulations of pressure preceding and +succeeding storms, and minute directions given for the hourly +observations of the necessary instruments. In the mean time we may here +remark that hourly observations under the circumstances above alluded to +are the more important when we consider that the barometer, the +instrument employed in observing these moving atmospheric masses, is +itself in motion. The ship may meet the accumulation of pressure and +sail through it transversely; or she may sail along it, the course of +the vessel being parallel to the line marking the highest pressure, the +ridge or crest of the wave; or the ship may make any angle with this +line: but whatever the circumstances may be under which she passes +through or along with such an accumulation of pressure, it should ever +be borne in mind that her position on the earth's surface is scarcely +ever the same at any one observation as it was at the preceding, the +barometer in the interval has changed _its_ position as well as the line +of maximum pressure, the rate of progress of which it is desirable to +observe. It will, therefore, be at once apparent that in order to obtain +the most accurate data on this head hourly observations are +indispensable. To these readings should of course be appended the places +of the ship from hour to hour, especially if she alter her course much. + +There is another point to which we wish to call attention in immediate +connexion with hourly readings--it is the observation of the instruments +on the days fixed for that purpose: they were originally suggested by +Sir John Herschel, whose directions should be strictly attended to: they +are as follows:-- + +The days fixed upon for these observations are the 21st of March, the +21st of June, the 21st of September, and the 21st of December, being +those, or immediately adjoining to those of the equinoxes and +solstices, in which the _solar influence_ is either stationary or in a +state of most rapid variation. _But should any one of those 21st days +fall on a Sunday, then it will be understood that the observations are +to be deferred till the next day, the 22nd._ The series of observations +on board each vessel should commence at 6 o'clock A.M. of the appointed +days, and terminate at 6 A.M. of the days following, according to the +usual reckoning of time adopted in the daily observations. + +In addition to the twenty-five hourly readings at the solstices and +equinoxes as above recommended, it would be desirable to continue the +observations until a complete elevation and depression of the barometer +had been observed at these seasons. This plan is adopted at the Royal +Observatory, Greenwich, and would be attended with this advantage were +it generally so--the progress of the elevation and depression would be +more readily traced and their velocities more accurately determined than +from the four or eight daily readings. + + +III.--LOCALITIES FOR ADDITIONAL OBSERVATIONS. + +In sketching out a system of barometric observation having especial +reference to the acquisition of data from which the _barometric +character_ of certain large areas of the surface of the globe may be +determined--inasmuch as such areas are distinguished from each other, on +the one hand by consisting of extensive spaces of the oceanic surface +unbroken, or scarcely broken, by land; on the other by the proximity of +such oceanic surface to large masses of land, and these masses +presenting two essentially different features, the one consisting of +land particularly characterized as continental, the other as insular, +regard has been accordingly had to such distribution of land and water. + +As these instructions have especial reference to observations at sea, +observations on land have not been alluded to; but in order that the +data accumulated may possess that value which is essential for carrying +on the inquiry in reference to atmospheric waves with success, provision +is made to mark out more distinctly the barometric effects of the +junction of large masses of land and water. It is well known that the +oceanic surface, and even the smaller surfaces of inland seas, produce +decided inflexions of the isothermal lines. They exercise an important +influence on temperature. It has also been shown that the neighbourhood +of water has a very considerable influence in increasing the +oscillations of the mercurial column in the barometer, and in the great +systems of European undulations it is well known that these oscillations +increase especially towards the north-west. The converse of this, +however, has not yet been subjected to observation; there has been no +systematic co-operation of observers for the purpose of determining the +barometric affections of large masses of water, such as the central +portion of the basin of the northern Atlantic, the portion of oceanic +surface between the Cape of Good Hope and Cape Horn, the Indian and +Southern oceans, and the vast basin of the Pacific. Nor are we yet +acquainted with the character of the oscillations, whether increasing or +decreasing, as we recede from the central portions of the oceanic +surfaces we have mentioned towards the land which forms their eastern, +western, or northern boundaries. This influence of the junction line of +land and water, so far as it is yet known, has been kept in view in +framing these instructions, and, as it appears so prominently in Europe, +it is hoped the additional observations between the four daily readings +to which probably many observers may habitually restrict themselves, +making on certain occasions and in particular localities a series of +observations at intervals of three hours, will not be considered too +frequent when the great importance of the problem to be solved is fully +apprehended. It need scarcely be said that the value of these +observations at three-hourly intervals will be greatly increased by the +number of observers co-operating in them. Upon such an extensive system +of co-operation a large space on the earth's surface, possessing +peculiarities which distinguish it from others extremely unlike it in +their general character, or assimilate it to such as possess with it +many features in common, is marked out below for particular observation, +occupying more than two-thirds of a zone in the northern hemisphere, +having a breadth of 40 deg., and including every possible variety of +terrestrial and aqueous surface, from the burning sands of the great +African desert, situated about the centre, to the narrow strip of land +connecting the two Americas on the one side, and the chain of islands +connecting China and Hindostan with Australia on the other. On each side +of the African continent we have spaces of open sea between 30 deg. and 40 deg. +west longitude north of the equator, and between 60 deg. and 80 deg. east +longitude, in or to the south of the equator, admirably suited for +contrasting the barometric affections, as manifested in these spaces of +open water, with those occurring in situations where the influence of +the terrestrial surface comes into more active operation. + +The localities where three-hourly readings are chiefly desirable may be +specified under the heads of _Northern Atlantic, Southern Atlantic, +Indian_ and _Southern Oceans,_ and _Pacific Ocean_. + + +_Northern Atlantic. Homeward-bound Voyages._--The discussion of +observations made in the United Kingdom and the western border of +central Europe, has indicated that off the north-west of Scotland a +centre of great barometric disturbance exists. This centre of +disturbance appears to be considerably removed from the usual tracks of +vessels crossing the Atlantic; nevertheless some light may be thrown on +the barometric phaenomena resulting from this disturbance by observations +during homeward-bound voyages, especially after the vessels have passed +the meridian of 50 deg. west longitude. Voyagers to or from Baffin and +Hudson bays would do well during the whole of the voyage to read off the +barometer every three hours, as their tracks would approach nearest the +centre of disturbance in question. Before crossing the 50th meridian, +the undulations arising from the distribution of land and water in the +neighbourhood of these vast inland seas would receive considerable +elucidation from the shorter intervals of observation, and after passing +the 50th meridian the extent of undulation, as compared with that +observed by the more southerly vessels, would be more distinctly marked +by the three-hourly series. Surveying vessels stationed on the +north-western coasts of Ireland and Scotland may contribute most +important information on this head by a regular and, as far as +circumstances will allow, an uninterrupted series either of six-hourly +or three-hourly observations. The intervals of observation on board +vessels stationed at the Western Isles, the Orkneys, and the Shetland +Isles, ought not to be longer than _three_ hours, principally on account +of the great extent of oscillation observed in those localities. Vessels +arriving from all parts of the world as they approach the United Kingdom +should observe at shorter intervals than six hours. As a general +instruction on this head the series of three-hourly observations may be +commenced on board vessels from America and the Pacific by the way of +Cape Horn on their passing the 20th meridian, such three-hourly +observations to be continued until the arrival of the vessels in port. +Ships by the way of the Cape of Good Hope should commence the +three-hourly series either on leaving or passing the colony, in order +that the phaenomena of the tropical depression hereafter to be noticed +may be well observed. + + +_Northern Atlantic. Outward-bound Voyages_.--Vessels sailing to the +United States, Mexico, and the West Indies, should observe at three +hours' interval upon passing the 60th meridian. Observations at this +interval, on board vessels navigating the Gulf of Mexico and the +Caribbean Sea, will be particularly valuable in determining the extent +of oscillation as influenced by the masses of land and water in this +portion of the torrid zone, as compared with the oscillation noticed off +the western coast of Africa, hereafter to be referred to. + + +_Southern Atlantic. Outward and homeward bound_.--Without doubt the most +interesting phaenomenon, and one that lies at the root of the great +atmospheric movements, especially those proceeding northwards in the +northern hemisphere and southwards in the southern, is the equatorial +depression first noticed by Von Humboldt and confirmed by many observers +since. We shall find the general expression of this most important +meteorological fact in the Report of the Committee of Physics and +Meteorology, appointed by the Royal Society in 1840, as follows: "The +barometer, at the level of the sea, does not indicate a mean atmospheric +pressure of equal amount in all parts of the earth; but, on the +contrary, the equatorial pressure is uniformly less in its mean amount +than at and beyond the tropics." Vessels that are outward bound should, +upon passing 40 deg. north latitude, commence the series of three-hourly +observations, with an especial reference to the equatorial depression. +These three-hourly observations should be continued until the latitude +of 40 deg. south has been passed: the whole series will then include the +minimum of the depression and the two maxima or apices forming its +boundaries. (See Daniell's 'Meteorological Essays,' 3rd edition.) In +passages across the equator, should the ships be delayed by calms, +opportunities should be embraced for observing this depression with +greater precision by means of _hourly_ readings; and these readings will +not only be valuable as respects the depression here spoken of, but will +go far to indicate the character of any disturbance that may arise, and +point out, as nearly as such observations will allow, the precise time +when such disturbance produced its effects in the neighbourhood of the +ships. In point of fact they will clearly illustrate the diversion of +the tendency to rise, spoken of in the Report before alluded to, as +resulting in ascending columns and sheets, between which wind flaws, +capricious in their direction and intensity, and often amounting to +sharp squalls, mark out the course of their feeders and the indraft of +cooler air from a distance to supply their void. Hourly observations, +with especial reference to this and the following head of inquiry, +should also be made off the western coast of Africa during the +homeward-bound voyage. + +Immediately connected with this part of the outward-bound voyage, hourly +observations, as often as circumstances will permit, while the ships are +sailing from the Madeiras to the equator, will be extremely valuable in +elucidating the origin of the great system of south-westerly atmospheric +waves that traverse Europe, and in furnishing data for comparison with +the amount of oscillation and other barometric phaenomena in the Gulf of +Mexico and the Caribbean Sea, a portion of the torrid zone essentially +different in its configuration and in the relations of its area to land +and water, as contra-distinguished to the northern portion of the +African continent; and these hourly observations are the more desirable +as the vessels may approach the land. They may be discontinued on +passing the equator, and the three-hourly series resumed. + +There are two points in the southern hemisphere, between 80 deg. west +longitude and 30 deg. east longitude, that claim particular attention in a +barometric point of view, viz., Cape Horn and the Cape of Good Hope; the +latter is within the area marked out for the three-hourly observations, +and too much attention cannot be paid to the indications of the +barometer as vessels are approaching or leaving the Cape. The northern +part of the South Atlantic Ocean has been termed the _true Pacific Ocean +of the world_; and at St. Helena a gale was scarcely ever known; it is +also said to be entirely free from actual storms (Col. Reid's 'Law of +Storms,' 1st edition, p. 415). It may therefore be expected that the +barometer will present in this locality but a small oscillation, and +ships in sailing from St. Helena to the Cape will do well to ascertain, +by means of the three-hourly observations, the increase of oscillation +as they approach the Cape. The same thing will hold good with regard to +Cape Horn: it appears from previous observation that a permanent +barometric depression exists in this locality, most probably in some way +connected with the immense depression noticed by Captain Sir James Clark +Ross, towards the Antarctic Circle. The general character of the +atmosphere off Cape Horn is also extremely different from its character +at St. Helena. It would therefore be well for vessels sailing into the +Pacific by Cape Horn, to continue the three-hourly observations until +the 90th meridian is passed. + +Before quitting the Atlantic Ocean it may be well to notice the marine +stations mentioned in my Third Report on Atmospheric Waves,[5] as being +particularly suitable for testing the views advanced in that report and +for tracing a wave of the south-westerly system from the most western +point of Africa to the extreme north of Europe. A series of hourly +observations off the western coast of Africa has already been suggested. +Vessels staying at Cape Verd Islands should not omit to make +observations at three hours' interval _during the whole of their stay_, +and when circumstances will allow, hourly readings. At the Canaries, +Madeiras, and the Azores, similar observations should be made. Vessels +touching at Cape Cantin, Tangier, Gibraltar, Cadiz, Lisbon, Oporto, +Corunna, and Brest, should also make these observations while they are +in the localities of these ports. At the Scilly Isles we have six-hourly +observations, made under the superintendence of the Honourable the +Corporation of the Trinity House. Ships in nearing these islands and +making the observations already pointed out, will greatly assist in +determining the increase of oscillation proceeding westward from the +nodal point of the two great European systems. We have already mentioned +the service surveying vessels employed on the coasts of Ireland and +Scotland may render, and the remaining portion of the area marked out in +the report may be occupied by vessels navigating the North Sea and the +coast of Norway, as far as Hammerfest. + +In connexion with these observations, having especial reference to the +European system of south-westerly atmospheric waves, the Mediterranean +presents a surface of considerable interest, both as regards these +particular waves, and the influence its waters exert in modifying the +two great systems of central Europe. The late Professor Daniell has +shown from the Manheim observations, that small undulations, having +their origin on the northern borders of the Mediterranean, have +propagated themselves northward, and in this manner, but in a smaller +degree, the waters of the Mediterranean have contributed to increase the +oscillation as well as the larger surface of the northern Atlantic. In +most of the localities of this great inland sea six-hourly observations +may suffice for this immediate purpose; but in sailing from Lisbon +through the Straits of Gibraltar, in the neighbourhood of Sicily and +Italy, and in the Grecian Archipelago, we should recommend the +three-hourly series, as marking more distinctly the effects resulting +from the proximity of land; this remark has especial reference to the +passage through the Straits of Gibraltar, where, if possible, hourly +observations should be made. + + +_The Indian and Southern Oceans. Outward and homeward bound._--On +sailing from the Cape of Good Hope to the East Indies, China, or +Australia, observations at intervals of three hours should be made until +the 40th meridian east is passed (homeward-bound vessels should commence +the three-hourly readings on arriving at this meridian). Upon leaving +the 40th meridian the six-hourly observations may be resumed on board +vessels bound for the Indies and China until they arrive at the equator, +when the readings should again be made at intervals of three hours, and +continued until the arrival of the vessels in port. With regard to +vessels bound for Australia and New Zealand, the six-hourly readings may +be continued from the 40th to the 100th meridian, and upon the vessels +passing the latter, the three-hourly readings should be commenced and +continued until the vessels arrive in port. Vessels navigating the +Archipelago between China and New Zealand, should make observations +every three hours, in order that the undulations arising from the +configuration of the terrestrial and oceanic surfaces may be more +distinctly marked and more advantageously compared with the Gulf of +Mexico, the Caribbean Sea, and the northern portion of the African +continent. + + +_The Pacific Ocean._--As this ocean presents so vast an aqueous surface, +generally speaking observations at intervals of six hours will be amply +sufficient to ascertain its leading barometric phaenomena. Vessels, +however, on approaching the continents of North and South America, or +sailing across the equator, should resort to the three-hourly readings, +in order to ascertain more distinctly the effect of the neighbourhood of +land on the oscillations of the barometer, as generally observed, over +so immense a surface of water in the one case, and the phaenomena of the +equatorial depression in the other: the same remarks relative to the +latter subject, which we offered under the head of South Atlantic, will +equally apply in the present instance. The configuration of the western +shores of North America renders it difficult to determine the precise +boundary where the three-hourly series should commence; the 90th +meridian is recommended for the boundary as regards South America, and +from this a judgment may be formed as to where the three-hourly +observations should commence in reference to North America. + + +In the previous sketch of the localities for the more important +observations, it will be seen that within the tropics there are three +which demand the greatest regard. + +I. The Archipelago between the two Americas, more particularly comprised +within the 40th and 120th meridians west longitude, and the equator and +the 40th degree of north latitude. As a general principle we should say +that vessels within this area should observe the barometer every three +hours. Its eastern portion includes the lower branches of the storm +paths, and on this account is peculiarly interesting, especially in a +barometric point of view. + +II. _The Northern portion of the African Continent, including the Sahara +or Great Desert._--This vast radiating surface must exert considerable +influence on the waters on each side northern Africa. Vessels sailing +within the area comprised between 40 deg. west and 70 deg. east, and the equator +and the 40th parallel, should also make observations at intervals of +three hours. + +III. _The great Eastern Archipelago._--This presents a somewhat similar +character to the western; like that, it is the region of terrific +hurricanes, and it becomes a most interesting object to determine its +barometric phaenomena; the three-hourly system of observation may +therefore be resorted to within an area comprised between the 70th and +140th meridians, and the equator and the 40th degree of north latitude. + +The southern hemisphere also presents three important localities, the +prolongations of the three tropical areas. It is unnecessary to enlarge +upon these, as ample instructions have been already given. We may, +however, remark, with regard to Australia, that three-hourly +observations should be made within the area comprised between the 100th +and 190th meridians east, and the equator and the 50th parallel south, +and hourly ones in the immediate neighbourhood of all its coasts. + + +IV.--STORMS, HURRICANES, AND TYPHOONS. + +The solution of the question--How far and in what manner are storms +connected with atmospheric waves?--must be extremely interesting to +every one engaged in either the naval or merchant service. As we have in +the former chapters directed attention to their connexion, our great +object here will be to endeavour to mark out such a line of observation +as appears most capable of throwing light, not only on the most +important desiderata as connected with storms, but also their connexion +or non-connexion with atmospheric waves. We shall accordingly +arrange this portion of the instructions under the following +heads:--_Desiderata_; _Localities_; _Margins_; _Preceding and Succeeding +Accumulations of Pressure._ + +_Desiderata._--The most important desiderata appertaining to the subject +of storms, are certainly their origin and termination. Of these initial +and terminal points in the course of great storms we absolutely know +nothing, unless _the white appearance of a round form_ observed by Mr. +Seymour on board the Judith and Esther, in lat. 17 deg. 19' north and long. +52 deg. 10' west (see Col. Reid's 'Law of Storms,' 1st edit. p. 65), may be +regarded as the commencement of the Antigua hurricane of August 2, 1837. +This vessel was the most eastern of those from which observations had +been obtained; and it is the absence of contemporaneous observations to +the eastward of the 50th meridian that leaves the question as to the +origin of the West Indian revolving storms unsolved. Not one of Mr. +Redfield's storm routes extends eastward of the 50th meridian; this at +once marks out, so far as storms are concerned, the entire space +included between the 20th and 50th meridians, the equator and the 60th +parallel, as a most suitable area for observations, under particular +circumstances hereafter to be noticed, with especial reference either to +the commencement or termination of storms, or the prolongation of Mr. +Redfield's storm paths. + +_Localities._--The three principal localities of storms are as +follows:--I. The western portion of the basin of the North Atlantic; II. +The China Sea and Bay of Bengal; and III. The Indian Ocean, more +particularly in the neighbourhood of Mauritius. The first two have +already been marked out as areas for the three-hourly observations; to +the latter, the remark as to extra observations under the head of +Desiderata will apply. + +_Margins._--Mr. Redfield has shown that on some occasions storms have +been preceded by an unusual pressure of the atmosphere; the barometer +has stood remarkably _high_, and it has hence been inferred that there +has existed _around_ the gale an accumulation of air forming a margin; +barometers placed under this margin indicating a much greater pressure +than the mean of the respective localities. With regard to the West +Indian and American hurricanes--any considerable increase of pressure, +especially within the space marked out to the eastward of the 50th +meridian, will demand immediate attention. Upon the barometer ranging +_very high_ within this space, three-hourly observations should be +immediately resorted to; and if possible, _hourly_ readings taken, and +this is the more important the nearer the vessel may be to the 50th +meridian. Each observation of the barometer should be accompanied by an +observation of the wind--its direction should be most carefully noted, +and the force estimated according to the scale in page 21, or by the +anemometer. It would be as well _at the time_ to project the barometric +readings in a curve even of a rough character, that the extent of fall +after the mercury had passed its maximum might be readily discernible by +the eye. A paper ruled in squares, the vertical lines representing the +commencement of hours, and the horizontal tenths of an inch, would be +quite sufficient for this purpose. The _force_ of the wind should be +noted at, or as near to the time of the passage of the maximum as +possible. During the fall of the mercury particular attention should be +paid to the manner in which the wind changes, should any change be +observed; and should the wind continue blowing steadily in _one_ +direction, but gradually _increasing_ in force, then such increments of +force should be most carefully noted. During the fall of the barometer, +should the changes of the wind and its increasing force indicate the +neighbourhood of a revolving storm, (independent of the obvious reasons +for avoiding the focus of the storm,) it would contribute as much to +increase our knowledge of these dangerous vortices to keep as near as +possible to their margins as to approach their centres. The recess from +the centre towards the margin of the storm, will probably be rendered +apparent by the _rising_ of the mercury; and so far as the observations +may be considered valuable for elucidating the connexion of atmospheric +waves with rotatory storms (other motives being balanced), it might be +desirable to keep the ship near the margin--provided she is not carried +beyond the influence of the winds which characterize the latter half of +the storm--until the barometer has nearly attained its usual elevation. +By this means some notion might be formed of the general direction of +the line of barometric pressure preceding or succeeding a storm. + +Should a gale be observed commencing without its having been preceded by +an unusual elevation of the mercurial column, and consequently no +additional observation have been made; when the force of the wind is +noted in the usual observations at or above 5, then the three-hourly +series should be resorted to, and the same care taken in noting the +direction, changes, and force of the wind as pointed out in the +preceding paragraph. + +The foregoing remarks relate especially to the central and western +portions of the North Atlantic; they will however equally apply to the +remaining localities of storms. Under any circumstances, and in any +locality, a _high_ barometer not less than a low one should demand +particular attention, and if possible, _hourly_ readings taken some time +before and after the passage of the maximum: this will be referred to +more particularly under the next head. + +_Preceding and Succeeding Accumulations of Pressure._--Mr. Redfield has +shown in his Memoir of the Cuba Hurricane of October, 1844, that two +associated storms were immediately preceded by a barometric wave, or +accumulation of pressure, the barometer rising above the usual or annual +mean. We have just referred to the importance of _hourly_ observations +on occasions of the readings being _high_ as capable of illustrating the +marginal phaenomena of storms, and in connexion with these accumulations +of pressure in advance of storms we would reiterate the suggestion. +These strips of accumulated pressure are doubtless crests of atmospheric +waves rolling forwards. In some cases a ship in its progress may cut +them transversely in a direction at right angles to their _length_, in +others very obliquely; but in all cases, whatever section may be given +by the curve representing the observations, too much attention cannot be +bestowed on the barometer, the wet and dry bulb thermometer, the +direction and force of the wind, the state of the sky, and the +appearance of the ocean during the ship's passage _through_ such an +accumulation of pressure. When the barometer attains its mean altitude, +and is rapidly rising above it in any locality, then _hourly_ +observations of the instruments and phaenomena above noticed should be +commenced and continued until after the mercury had attained its highest +point and had sunk again to its mean state. In such observations +particular attention should be paid to the direction and force of the +wind preceding the barometric maximum--and the same phaenomena succeeding +it, and particular notice should be taken of the time when, and amount +of any change either in the direction or force of the wind. It is by +such observations as these, carried on with great care and made at every +accessible portion of the oceanic surface, that we may be able to +ascertain the continuity of these atmospheric waves, to determine +somewhat respecting their length, to show the character of their +connexion with the rotatory storm, and to deduce the direction and rate +of their progress. + + +V.--SEASONS FOR EXTRA OBSERVATIONS. + +In reference to certain desiderata that have presented themselves in the +course of my researches on this subject (see Report of the British +Association for the Advancement of Science, 1846, p. 163), the _phases_ +of the larger barometric undulations, and the _types_ of the various +seasons of the year, demand particular attention and call for extra +observations at certain seasons: of these, three only have yet been +ascertained--the type for the middle of November--the annual depression +on or about the 28th of November--and the annual elevation on or about +the 25th of December. The enunciation of the first is as under: "That +during fourteen days in November, more or less equally disposed about +the middle of the month, the oscillations of the barometer exhibit a +remarkably symmetrical character, that is to say, the fall succeeding +the transit of the maximum or the highest reading is to a great extent +similar to the preceding rise. This rise and fall is not continuous or +unbroken; in some cases it consists of _five_, in others of _three_ +distinct elevations. The complete rise and fall has been termed the +great symmetrical barometric wave of November. At its setting in the +barometer is generally low, sometimes below twenty-nine inches. This +depression is generally succeeded by _two_ well-marked undulations, +varying from one to two days in duration. The central undulation, which +also forms the apex of the great wave, is of larger extent, occupying +from three to five days; when this has passed, two smaller undulations +corresponding to those at the commencement of the wave make their +appearance, and at the close of the last the wave terminates." With but +slight exceptions, the observations of eight successive years have +confirmed the general correctness of this type. On two occasions the +central apex has not been the highest, and these deviations, with some +of a minor character, form the exceptions alluded to. This type only has +reference to London and the south-eastern parts of England; proceeding +westward, north-westward, and northward, the symmetrical character of +this type is considerably departed from; each locality possessing its +own type of the barometric movements during November. The desiderata in +immediate connexion with the November movements, as observed in the +southern and south-eastern parts of England, that present themselves, +are--the determination of the types for November, especially its middle +portion, as exhibited on the oceanic surface within an area comprised +between the 30th and 60th parallels, and the 1st and 40th meridians +west. Vessels sailing within this area may contribute greatly to the +determination of these types by making observations at intervals of +three hours from the 1st of November to the 7th or 8th of December. The +entire period of the great symmetrical wave of November will most +probably be embraced by such a series of observations, as well as the +annual depression of the 28th. For the elevation of the 25th of December +the three-hourly observations should be commenced on the 21st, and +continued until the 3rd or 4th of the succeeding January. + +With respect to the great wave of November, our knowledge of it would be +much increased by such a series of observations as mentioned above, +being made on board surveying and other vessels employed off Scotland +and Ireland; vessels navigating the North Sea; vessels stationed off the +coasts of France, Spain, Portugal, and the northern parts of Africa, and +at all our stations in the Mediterranean. In this way the area of +examination would be greatly enlarged, and the _differences_ of the +curves more fully elucidated; and this extended area of observation is +the more desirable, as there is some reason to believe that the line of +greatest symmetry _revolves_ around a fixed point, most probably the +nodal point of the great European systems. + +It is highly probable that movements of a somewhat similar character, +although presenting very different curves, exist in the southern +hemisphere. The November wave is more or less associated with storms. It +has been generally preceded by a high barometer and succeeded by a low +one, and this low state of the barometer has been accompanied by stormy +weather. We are therefore prepared to seek for similar phaenomena in the +southern hemisphere, in those localities which present similar states of +weather, and at seasons when such weather predominates. We have already +marked out the two capes in the Southern hemisphere for three-hourly +observations: they must doubtless possess very peculiar barometric +characters, stretching as they do into the vast area of the Southern +Ocean. It is highly probable that the oscillations, especially at some +seasons, are very considerable, and vessels visiting them at such +seasons would do well to record with especial care the indications of +the instruments already alluded to. At present we know but little of the +barometric movements in the Southern hemisphere, and every addition to +our knowledge in this respect will open the way to more important +conclusions. + +It has been observed in the south-east of England that the barometer has +generally passed a maximum on or about the 3rd of every month, and this +has been so frequently the case as to form the rule rather than the +exception. The same fact during a more limited period has been observed +at Toronto. With especial reference to this subject the three-hourly +series of observations may be resorted to in all localities, but +especially north of the 40th parallel in the northern hemisphere. They +should be commenced at midnight immediately preceding the 1st and +continued to midnight succeeding the 5th. + + + + +CHAPTER IV. + +PRACTICAL DIRECTIONS FOR AVOIDING THE CENTRES OF ROTATING +STORMS. + + +Figures 1 and 2, enlarged and printed on narrow rings of stiff +cardboard, are employed for this purpose. The letters outside the thick +circle are intended to distinguish the points of the compass, and in use +should always coincide with those points on the chart. The letters +within the thick circle indicate the direction of the wind in a +hurricane, the whirl being shown by the arrows between the letters. In +the northern hemisphere the direction of the whirl is always contrary to +that in which the hands of a watch move, and in the southern coincident +thereto. The graduation is intended to assist the mariner in +ascertaining the bearing of the centre of a storm from his ship. + + +_Use._ + +At any time when a severe gale or hurricane is expected, the seaman +should at once find the position of his ship on the chart, and place +upon it the graduated point which answers to the direction of the wind +at the time, taking care that the needle is directed to the north, so +that the exterior letters may point on the chart to the respective +points of the compass: this is very essential. This simple process will +at once acquaint the seaman with two important facts relative to the +coming hurricane--his position in the storm, and the direction in +which it is moving. + + +_Examples._ + +A captain of a ship in latitude 35 deg. 24' N., longitude 64 deg. 12' W., bound +to the United States, observes the barometer to stand unusually high, +say 30.55 inches: shortly after the mercury begins to fall, at first +slowly and steadily; as the glass falls the wind freshens, and is +noticed to blow with increasing force from the S. so as to threaten a +gale. The position of the ship on the chart is now to be found, and the +graduated point under the letters E. S. is to be placed thereon, +taking care to direct the needle to the north. From these two +circumstances, the falling barometer and the wind blowing from the south +with increasing force, the mariner is aware of this simple fact, that he +is situated in the advancing portion of a body of air which is +proceeding towards the N.E.; and if he turn his face to the N.E. he will +find he is on the right of the axis line, or line cutting the advancing +body transversely. The hurricane circle as it lies on the chart reveals +to him another important fact, which is, that if he pursue his course he +will sail _towards_ the axis line of the hurricane, and may stand a +chance of foundering in its centre. To avoid this he has one of two +courses to adopt; either to lay-to on the _starboard tack_, according to +Col. Reid's rules (see his 'Law of Storms,' 1st edit., pp. 425 to 428), +the ship being in the right-hand semicircle of the hurricane, or so to +alter his course as to keep without the influence of the storm. In the +present case the adoption of the latter alternative would involve a +reversal of his former course; nevertheless it is clear the more he +bears to the S.E. the less he will experience the violence of the +hurricane: should he heave his ship to, upon moving the hurricane circle +from the ship's place on the chart towards the N.E., he will be able to +judge of the changes of the wind he is likely to experience: thus it +will first veer to S.S.W., the barometer still falling; then to S.W., +the barometer at a minimum--this marks the position of the most violent +portion of the storm he may be in, and by keeping the barometer as high +as he can by bearing towards the S.E., the farther he will be from the +centre--the barometer now begins to rise, the wind veering to W.S.W., +and the hurricane finally passes off with the wind at W. It is to be +particularly remarked that in this example the ship is in the _most +dangerous quadrant_, as by scudding she would be driven in advance of +the track of the storm's centre, which of course would be approaching +her. + +Assuming that the hurricane sets in at the ship's place with the wind at +S.E., the proceeding will be altogether different. At first the wind is +fair for the prosecution of the voyage, and it is desirable to take +advantage of this fair wind to avoid as much as possible the track of +the centre, which passes over the ship's place in this instance, and is +always the most dangerous part of the storm. As the ship is able to make +good distance from this track by bearing towards the N.W., provided she +has plenty of sea-room, she will experience less of the violence of the +hurricane; but as most of the Atlantic storms sweep over the shore, it +will be desirable to lay-to at some point on the _larboard tack_, the +ship being now in the left-hand semicircle. By moving the circle as +before directed it will be seen that the veering of the wind is now +E.S.E., E., E.N.E., N.E., the lowest barometer N.N.E., N., and N.N.W., +the ship experiencing more or less of these changes as it is nearer to +or farther from the axis line. + +In latitudes lower than 20 deg. N. the Atlantic hurricanes usually move +towards the N.W. Taking the same positions of our ship with regard to +the storms as in the two former examples, if the storm set in with the +wind E. the proper proceeding is to bear away for the N.E., the most +dangerous quadrant of the hurricane having overtaken the ship, the +veering of the wind if she is lying-to will be E., E.S.E., S.E., with +the lowest barometer S.S.E. and S. Should the storm set in at N.E., her +position at the time will be some indication of the distance of the +centre's track from the nearest land, and will greatly assist in +determining the point at which the captain ought to lay-to after taking +advantage of the N.E. wind, should he be able so to do, to bear away +from the centre line, so as to avoid as much as possible the violence of +the storm. From the proximity of the West Indian Islands to this +locality of the storm-paths, the danger is proportionally increased. + +The above examples have reference only to the lower and upper branches +of the storm paths of the Northern Atlantic in the neighbourhood of the +West Indies and the United States. In latitudes from about 25 deg. to 32 deg. +these paths usually _re-curve_, and at some point will move towards the +north. The veering of the wind will consequently be more or less +complicated according as the ship may be nearer to or farther from the +centre. The tables on page 11, combined with the first of those +immediately following the next paragraph, will, it is hoped, prove +advantageous in assisting the mariner as to the course to be adopted. As +a general principle we should say it would be best to bear to the +eastward, so as not only to avoid the greater fury of the storm, but to +get into the S. and S.W. winds, which give the principal chances of +making a westerly course. + +We have in page 44 called attention to the fact that the storm paths +traced by Mr. Redfield do not extend eastward of the 50th meridian. This +by no means precludes the existence of severe storms and those of a +rotatory character in the great basin of the Northern Atlantic, +especially between the 40th and 50th parallels. A remarkable instance +has come under the author's attention of the wind hauling _apparently_ +contrary to the usual theory: it may be that the storm route was in a +direction not generally observed. We are at the present moment destitute +of any information that at all indicates a _reversion_ of the rotation +in either hemisphere. The following tables constructed for the northern +hemisphere, and for storm routes _not yet ascertained_, may probably be +consulted with advantage on anomalous occasions. + + +HURRICANE MOVING FROM SOUTH TO NORTH. + + Axis line, wind E., barometer falling, first half of storm. + Axis line, wind W., barometer rising, last half of storm. + + +RIGHT-HAND SEMICIRCLE. + + Wind E.S.E., S.E., S.S.E., S., barometer falling, first half of storm. + Wind W.S.W., S.W., S.S.W., S., barometer rising, last half of storm. + +LEFT-HAND SEMICIRCLE. + + Wind E.N.E., N.E., N.N.E., N., barometer falling, first half of storm. + Wind W.N.W., N.W., N.N.W., N., barometer rising, last half of storm. + + +HURRICANE MOVING FROM NORTH TO SOUTH. + + Axis line, wind W., barometer falling, first half of storm. + Axis line, wind E., barometer rising, last half of storm. + + +RIGHT-HAND SEMICIRCLE. + + Wind W.N.W., N.W., N.N.W., N., barometer falling, first half of storm. + Wind E.N.E., N.E., N.N.E., N., barometer rising, last half of storm. + + +LEFT-HAND SEMICIRCLE. + + Wind W.S.W., S.W., S.S.W., S., barometer falling, first half of storm. + Wind E.S.E., S.E., S.S.E., S,, barometer rising, last half of storm. + + +HURRICANE MOVING PROM WEST TO EAST. + + Axis line, wind S., barometer falling, first half of storm. + Axis line, wind N., barometer rising, last half of storm. + + +RIGHT-HAND SEMICIRCLE. + + Wind S.S.W., S.W., W.S.W., W., barometer falling, first half of storm. + Wind N.N.W., N.W., W.N.W., W., barometer rising, last half of storm. + + +LEFT-HAND SEMICIRCLE. + + Wind S.S.E., S.E., E.S.E., E., barometer falling, first half of storm. + Wind N.N.E., N.E., E.N.E., E., barometer rising, last half of storm. + +HURRICANE MOVING FROM NORTH-WEST TO SOUTH-EAST. + + Axis line, wind S.W., barometer falling, first half of storm. + Axis line, wind N.E., barometer rising, last half of storm. + + +RIGHT-HAND SEMICIRCLE. + + Wind W.S.W., W., W.N.W., N.W., barometer falling, first half of storm. + Wind N.N.E., N., N.N.W., N.W., barometer rising, last half of storm. + + +LEFT-HAND SEMICIRCLE. + + Wind S.S.W., S., S.S.E., S.E., barometer falling, first half of storm. + Wind E.N.E., E., E.S.E., S.E., barometer rising, last half of storm. + + + + +APPENDIX. + +TABLE I.--Correction to be added to Barometers for Capillary Action. + + +--------------------+---------------------------------+ + | | Correction for | + | Diameter of Tube. |-----------------+---------------| + | | Unboiled Tubes. | Boiled Tubes. | + |--------------------|-----------------|---------------| + | Inch. | Inch. | Inch. | + | 0.60 | 0.004 | 0.002 | + | 0.50 | 0.007 | 0.003 | + | 0.45 | 0.010 | 0.005 | + | 0.40 | 0.014 | 0.007 | + | 0.35 | 0.020 | 0.010 | + | 0.30 | 0.028 | 0.014 | + | 0.25 | 0.040 | 0.020 | + | 0.20 | 0.060 | 0.029 | + | 0.15 | 0.088 | 0.044 | + | 0.10 | 0.142 | 0.070 | + +--------------------+-----------------+---------------+ + + ++---------------------------------------------------------------------+ +|Transcibers note: The following 100 line table has been split into | +|two, both vertically and horizontally, so that it can be accommodated| +|on these pages. | ++---------------------------------------------------------------------+ + + +TABLE II.--Correction to be applied to Barometers with _Brass Scales_, +extending from the Cistern to the top of the Mercurial Column, to reduce +the observation to 32 deg. Fahrenheit. + + + ---+------------------------------------------------------------+---- + | I N C H E S. | + T | -----+-------+------+-------+------+-------+------+--------| T + e | | | | | | | | | e + m | 24 | 24.5 | 25 | 25.5 | 26 | 26.5 | 27 | 27.5 | m + p | | | | | | | | | p + ---+------+-------+------+-------+------+-------+------+--------+---- + deg. | + | + | + | + | + | + | + | + | deg. + 0 | .061 | .063 | .064 | .065 | .067 | .068 | .069 | .071 | 0 + 1 | .059 | .061 | .062 | .063 | .064 | .065 | .067 | .068 | 1 + 2 | .057 | .058 | .060 | .061 | .062 | .063 | .064 | .066 | 2 + 3 | .055 | .056 | .057 | .059 | .060 | .061 | .062 | .063 | 3 + 4 | .053 | .054 | .055 | .056 | .057 | .058 | .059 | .061 | 4 + 5 | .051 | .052 | .053 | .054 | .055 | .056 | .057 | .058 | 5 + 6 | .049 | .050 | .051 | .052 | .053 | .054 | .055 | .056 | 6 + 7 | .046 | .047 | .048 | .049 | .050 | .051 | .052 | .053 | 7 + 8 | .044 | .045 | .046 | .047 | .048 | .049 | .050 | .051 | 8 + 9 | .042 | .043 | .044 | .045 | .046 | .046 | .047 | .048 | 9 + 10 | .040 | .041 | .042 | .042 | .043 | .044 | .045 | .046 | 10 + | | | | | | | | | + 11 | .038 | .039 | .039 | .040 | .041 | .042 | .042 | .043 | 11 + 12 | .036 | .036 | .037 | .038 | .039 | .039 | .040 | .041 | 12 + 13 | .033 | .034 | .035 | .036 | .036 | .037 | .038 | .038 | 13 + 14 | .031 | .032 | .033 | .033 | .034 | .035 | .035 | .036 | 14 + 15 | .029 | .030 | .030 | .031 | .032 | .032 | .033 | .033 | 15 + 16 | .027 | .028 | .028 | .029 | .029 | .030 | .030 | .031 | 16 + 17 | .025 | .025 | .026 | .026 | .027 | .027 | .028 | .028 | 17 + 18 | .023 | .023 | .024 | .024 | .025 | .025 | .025 | .026 | 18 + 19 | .021 | .021 | .021 | .022 | .022 | .023 | .023 | .024 | 19 + 20 | .018 | .019 | .019 | .020 | .020 | .020 | .021 | .021 | 20 + | | | | | | | | | + 21 | .016 | .017 | .017 | .017 | .018 | .018 | .018 | .019 | 21 + 22 | .014 | .014 | .015 | .015 | .015 | .016 | .016 | .016 | 22 + 23 | .012 | .012 | .012 | .013 | .013 | .013 | .013 | .014 | 23 + 24 | .010 | .010 | .010 | .010 | .011 | .011 | .011 | .011 | 24 + 25 | .008 | .008 | .008 | .008 | .008 | .008 | .009 | .009 | 25 + 26 | .005 | .006 | .006 | .006 | .006 | .006 | .006 | .006 | 26 + 27 | .003 | .003 | .003 | .003 | .004 | .004 | .004 | .004 | 27 + 28 | .001 | .001 | .001 | .001 | .001 | .001 | .001 | .001 | 28 + | -- | -- | -- | -- | -- | -- | -- | -- | + 29 | .001 | .001 | .001 | .001 | .001 | .001 | .001 | .001 | 29 + 30 | .003 | .003 | .003 | .004 | .004 | .004 | .004 | .004 | 30 + | | | | | | | | | + 31 | .005 | .006 | .006 | .006 | .006 | .006 | .006 | .006 | 31 + 32 | .008 | .008 | .008 | .008 | .008 | .008 | .008 | .009 | 32 + 33 | .010 | .010 | .010 | .010 | .011 | .011 | .011 | .011 | 33 + 34 | .012 | .012 | .012 | .013 | .013 | .013 | .013 | .014 | 34 + 35 | .014 | .014 | .015 | .015 | .015 | .015 | .016 | .016 | 35 + 36 | .016 | .017 | .017 | .017 | .017 | .018 | .018 | .019 | 36 + 37 | .018 | .019 | .019 | .019 | .020 | .020 | .021 | .021 | 37 + 38 | .020 | .021 | .021 | .022 | .022 | .023 | .023 | .023 | 38 + 39 | .023 | .023 | .024 | .024 | .024 | .025 | .025 | .026 | 39 + 40 | .025 | .025 | .026 | .026 | .027 | .027 | .028 | .028 | 40 + | | | | | | | | | + 41 | .027 | .027 | .028 | .029 | .029 | .030 | .030 | .031 | 41 + 42 | .029 | .030 | .030 | .031 | .031 | .032 | .033 | .033 | 42 + 43 | .031 | .032 | .032 | .033 | .034 | .034 | .035 | .036 | 43 + 44 | .033 | .034 | .035 | .035 | .036 | .037 | .037 | .038 | 44 + 45 | .035 | .036 | .037 | .038 | .038 | .039 | .040 | .041 | 45 + 46 | .038 | .038 | .039 | .040 | .041 | .042 | .042 | .043 | 46 + 47 | .040 | .041 | .041 | .042 | .043 | .044 | .045 | .046 | 47 + 48 | .042 | .043 | .044 | .045 | .045 | .046 | .047 | .048 | 48 + 49 | .044 | .045 | .046 | .047 | .043 | .049 | .050 | .050 | 49 + 50 | .046 | .047 | .043 | .049 | .050 | .051 | .052 | .053 | 50 + ---+------+-------+------+-------+------+-------+------+--------+---- + + ---+-----------------------------------------------------+---- + | I N C H E S. | + T |-------+------+-------+------+-------+------+--------| T + e | | | | | | | | e + m | 28 | 28.5 | 29 | 29.5 | 30 | 30.5 | 31 | m + p | | | | | | | | p + ---+-------+------+-------+------+-------+------+--------+---- + deg. | + | + | + | + | + | + | + | deg. + 0 | .072 | .073 | .074 | .076 | .077 | .078 | .080 | 0 + 1 | .069 | .071 | .072 | .073 | .074 | .076 | .077 | 1 + 2 | .067 | .068 | .069 | .070 | .072 | .073 | .074 | 2 + 3 | .064 | .065 | .067 | .068 | .069 | .070 | .071 | 3 + 4 | .062 | .063 | .064 | .065 | .066 | .067 | .068 | 4 + 5 | .039 | .060 | .061 | .062 | .063 | .065 | .066 | 5 + 6 | .057 | .058 | .059 | .060 | .061 | .062 | .063 | 6 + 7 | .054 | .055 | .056 | .057 | .058 | .059 | .060 | 7 + 8 | .052 | .053 | .054 | .054 | .055 | .056 | .057 | 8 + 9 | .049 | .050 | .051 | .052 | .053 | .054 | .054 | 9 + 10 | .047 | .047 | .048 | .049 | .050 | .051 | .052 | 10 + | | | | | | | | + 11 | .044 | .045 | .046 | .046 | .047 | .048 | .049 | 11 + 12 | .042 | .042 | .043 | .044 | .045 | .045 | .046 | 12 + 13 | .039 | .040 | .040 | .041 | .042 | .043 | .043 | 13 + 14 | .037 | .037 | .038 | .038 | .039 | .040 | .040 | 14 + 15 | .034 | .035 | .035 | .036 | .036 | .037 | .038 | 15 + 16 | .032 | .032 | .033 | .033 | .034 | .034 | .035 | 16 + 17 | .029 | .030 | .030 | .031 | .031 | .032 | .032 | 17 + 18 | .026 | .027 | .027 | .028 | .028 | .029 | .029 | 18 + 19 | .024 | .024 | .025 | .025 | .026 | .026 | .027 | 19 + 20 | .021 | .022 | .022 | .023 | .023 | .023 | .024 | 20 + | | | | | | | | + 21 | .019 | .019 | .020 | .020 | .020 | .021 | .021 | 21 + 22 | .016 | .017 | .017 | .017 | .018 | .018 | .018 | 22 + 23 | .014 | .014 | .014 | .015 | .015 | .015 | .015 | 23 + 24 | .011 | .012 | .012 | .012 | .012 | .012 | .013 | 24 + 25 | .009 | .009 | .009 | .009 | .009 | .010 | .010 | 25 + 26 | .006 | .006 | .007 | .007 | .007 | .007 | .007 | 26 + 27 | .004 | .004 | .004 | .004 | .004 | .004 | .004 | 27 + 28 | .001 | .001 | .001 | .001 | .001 | .001 | .001 | 28 + | -- | -- | -- | -- | -- | -- | -- | + 29 | .001 | .001 | .001 | .001 | .001 | .001 | .001 | 29 + 30 | .004 | .004 | .004 | .004 | .004 | .004 | .004 | 30 + | | | | | | | | + 31 | .006 | .006 | .007 | .007 | .007 | .007 | .007 | 31 + 32 | .009 | .009 | .009 | .009 | .009 | .010 | .010 | 32 + 33 | .011 | .012 | .012 | .012 | .012 | .012 | .012 | 33 + 34 | .014 | .014 | .014 | .015 | .015 | .015 | .015 | 34 + 35 | .016 | .017 | .017 | .017 | .018 | .018 | .018 | 35 + 36 | .019 | .019 | .020 | .020 | .020 | .021 | .021 | 36 + 37 | .021 | .022 | .022 | .022 | .023 | .023 | .024 | 37 + 38 | .024 | .024 | .025 | .025 | .026 | .026 | .026 | 38 + 39 | .026 | .027 | .027 | .028 | .028 | .029 | .029 | 39 + 40 | .029 | .029 | .030 | .030 | .031 | .031 | .032 | 40 + | | | | | | | | + 41 | .031 | .032 | .033 | .033 | .034 | .034 | .035 | 41 + 42 | .034 | .034 | .035 | .036 | .036 | .037 | .037 | 42 + 43 | .036 | .037 | .038 | .038 | .039 | .010 | .040 | 43 + 44 | .039 | .040 | .040 | .041 | .042 | .042 | .043 | 44 + 45 | .041 | .042 | .043 | .044 | .044 | .045 | .046 | 45 + 46 | .044 | .045 | .045 | .046 | .047 | .048 | .049 | 46 + 47 | .046 | .047 | .048 | .049 | .050 | .051 | .051 | 47 + 48 | .049 | .050 | .051 | .052 | .052 | .053 | .054 | 48 + 49 | .031 | .052 | .053 | .054 | .055 | .056 | .057 | 49 + 50 | .054 | .055 | .056 | .057 | .058 | .059 | .060 | 50 + ---+-------+------+-------+------+-------+------+--------+---- + + +TABLE II.--_Continued_ + + ----+------------------------------------------------------------+----- + | I N C H E S. | + T |------+-------+------+-------+------+-------+------+--------| T + e | | | | | | | | | e + m | 24 | 24.5 | 25 | 25.5 | 26 | 26.5 | 27 | 27.5 | m + p | | | | | | | | | p + ----+------+-------+------+-------+------+-------+------+--------+----- + deg. | + | + | + | + | + | + | + | + | deg. + 51 | .048 | .049 | .050 | .051 | .052 | .053 | .054 | .055 | 51 + 52 | .050 | .052 | .053 | .054 | .055 | .056 | .057 | .058 | 52 + 53 | .053 | .054 | .055 | .056 | .057 | .058 | .059 | .060 | 53 + 54 | .055 | .056 | .057 | .053 | .059 | .060 | .062 | .063 | 54 + 55 | .057 | .058 | .059 | .060 | .062 | .063 | .064 | .065 | 55 + 56 | .059 | .060 | .061 | .063 | .064 | .065 | .066 | .063 | 56 + 57 | .061 | .062 | .064 | .065 | .066 | .068 | .069 | .070 | 57 + 58 | .063 | .065 | .066 | .067 | .069 | .070 | .071 | .073 | 58 + 59 | .065 | .067 | .068 | .070 | .071 | .072 | .074 | .075 | 59 + 60 | .068 | .069 | .070 | .072 | .073 | .075 | .076 | .077 | 60 + | | | | | | | | | + 61 | .070 | .071 | .073 | .074 | .075 | .077 | .078 | .080 | 61 + 62 | .072 | .073 | .075 | .076 | .078 | .079 | .081 | .082 | 62 + 63 | .074 | .076 | .077 | .079 | .080 | .082 | .083 | .085 | 63 + 64 | .076 | .073 | .079 | .081 | .082 | .084 | .086 | .087 | 64 + 65 | .078 | .080 | .082 | .083 | .085 | .086 | .088 | .090 | 65 + 66 | .080 | .082 | .084 | .085 | .087 | .089 | .090 | .092 | 66 + 67 | .083 | .084 | .086 | .088 | .089 | .091 | .093 | .095 | 67 + 68 | .085 | .086 | .088 | .090 | .092 | .094 | .095 | .097 | 68 + 69 | .087 | .089 | .090 | .092 | .094 | .096 | .098 | .100 | 69 + 70 | .089 | .091 | .093 | .095 | .096 | .098 | .100 | .102 | 70 + | | | | | | | | | + 71 | .091 | .093 | .095 | .097 | .099 | .101 | .102 | .104 | 71 + 72 | .093 | .095 | .097 | .099 | .101 | .103 | .105 | .107 | 72 + 73 | .095 | .097 | .099 | .101 | .103 | .105 | .107 | .109 | 73 + 74 | .097 | .099 | .102 | .104 | .106 | .108 | .110 | .112 | 74 + 75 | .100 | .102 | .104 | .106 | .108 | .110 | .112 | .114 | 75 + 76 | .102 | .104 | .106 | .108 | .110 | .112 | .114 | .117 | 76 + 77 | .104 | .106 | .108 | .110 | .112 | .115 | .117 | .119 | 77 + 78 | .106 | .108 | .110 | .113 | .115 | .117 | .119 | .122 | 78 + 79 | .108 | .110 | .113 | .115 | .117 | .119 | .122 | .124 | 79 + 80 | .110 | .113 | .115 | .117 | .119 | .122 | .124 | .126 | 80 + | | | | | | | | | + 81 | .112 | .115 | .117 | .119 | .122 | .124 | .126 | .129 | 81 + 82 | .114 | .117 | .119 | .122 | .124 | .126 | .129 | .131 | 82 + 83 | .117 | .119 | .121 | .124 | .126 | .129 | .131 | .134 | 83 + 84 | .119 | .121 | .124 | .126 | .129 | .131 | .134 | .136 | 84 + 85 | .121 | .123 | .136 | .128 | .131 | .133 | .136 | .139 | 85 + 86 | .123 | .126 | .128 | .131 | .133 | .136 | .138 | .141 | 86 + 87 | .125 | .128 | .130 | .133 | .136 | .138 | .141 | .143 | 87 + 88 | .127 | .130 | .133 | .133 | .138 | .141 | .143 | .146 | 88 + 89 | .129 | .132 | .135 | .137 | .140 | .143 | .146 | .148 | 89 + 90 | .131 | .134 | .137 | .140 | .142 | .145 | .148 | .151 | 90 + | | | | | | | | | + 91 | .134 | .136 | .139 | .142 | .145 | .148 | .150 | .153 | 91 + 92 | .136 | .139 | .141 | .144 | .147 | .150 | .153 | .156 | 92 + 93 | .138 | .141 | .144 | .147 | .149 | .152 | .155 | .158 | 93 + 94 | .140 | .143 | .146 | .149 | .152 | .155 | .157 | .161 | 94 + 95 | .142 | .145 | .148 | .151 | .154 | .157 | .160 | .163 | 95 + 96 | .144 | .147 | .150 | .153 | .156 | .159 | .162 | .165 | 96 + 97 | .146 | .149 | .152 | .155 | .159 | .162 | .165 | .168 | 97 + 98 | .148 | .152 | .155 | .158 | .161 | .164 | .167 | .170 | 98 + 99 | .151 | .154 | .157 | .160 | .163 | .166 | .169 | .173 | 99 + 100 | .153 | .156 | .159 | .162 | .165 | .169 | .172 | .175 | 100 + ----+------+-------+------+-------+------+-------+------+--------+----- + + + ----+-----------------------------------------------------+----- + | I N C H E S. | + T |-------+------+-------+------+-------+------+--------| T + e | | | | | | | | e + m | 28 | 28.5 | 29 | 29.5 | 30 | 30.5 | 31 | m + p | | | | | | | | p + ----+-------+------+-------+------+-------+------+--------+----- + deg. | + | + | + | + | + | + | + | deg. + 51 | .056 | .057 | .058 | .059 | .060 | .061 | .062 | 51 + 52 | .059 | .060 | .061 | .062 | .063 | .064 | .065 | 52 + 53 | .061 | .063 | .064 | .065 | .066 | .067 | .068 | 53 + 54 | .064 | .065 | .066 | .067 | .068 | .070 | .071 | 54 + 55 | .066 | .068 | .069 | .070 | .071 | .072 | .073 | 55 + 56 | .069 | .070 | .071 | .073 | .074 | .075 | .076 | 56 + 57 | .071 | .073 | .074 | .075 | .076 | .078 | .079 | 57 + 58 | .074 | .075 | .077 | .078 | .079 | .081 | .082 | 58 + 59 | .076 | .078 | .079 | .080 | .082 | .083 | .085 | 59 + 60 | .079 | .080 | .082 | .083 | .085 | .086 | .087 | 60 + | | | | | | | | + 61 | .081 | .083 | .084 | .086 | .087 | .089 | .090 | 61 + 62 | .084 | .085 | .087 | .088 | .090 | .091 | .093 | 62 + 63 | .086 | .088 | .089 | .091 | .093 | .094 | .096 | 63 + 64 | .089 | .090 | .092 | .094 | .095 | .097 | .098 | 64 + 65 | .091 | .093 | .095 | .096 | .098 | .100 | .101 | 65 + 66 | .094 | .096 | .097 | .099 | .101 | .102 | .104 | 66 + 67 | .096 | .098 | .100 | .102 | .103 | .105 | .107 | 67 + 68 | .099 | .101 | .102 | .104 | .106 | .108 | .109 | 68 + 69 | .101 | .103 | .105 | .107 | .109 | .110 | .112 | 69 + 70 | .104 | .106 | .108 | .109 | .111 | .113 | .115 | 70 + | | | | | | | | + 71 | .106 | .108 | .110 | .112 | .114 | .116 | .118 | 71 + 72 | .109 | .111 | .113 | .115 | .117 | .119 | .120 | 72 + 73 | .111 | .113 | .115 | .117 | .119 | .121 | .123 | 73 + 74 | .114 | .116 | .118 | .120 | .122 | .124 | .126 | 74 + 75 | .116 | .118 | .120 | .122 | .125 | .127 | .129 | 75 + 76 | .119 | .121 | .123 | .125 | .127 | .129 | .131 | 76 + 77 | .121 | .123 | .126 | .128 | .130 | .132 | .134 | 77 + 78 | .124 | .126 | .128 | .130 | .133 | .135 | .137 | 78 + 79 | .126 | .128 | .131 | .133 | .135 | .137 | .140 | 79 + 80 | .129 | .131 | .133 | .136 | .138 | .140 | .143 | 80 + | | | | | | | | + 81 | .131 | .134 | .136 | .138 | .141 | .143 | .145 | 81 + 82 | .134 | .136 | .138 | .141 | .143 | .146 | .148 | 82 + 83 | .136 | .139 | .141 | .143 | .146 | .148 | .151 | 83 + 84 | .139 | .141 | .144 | .146 | .149 | .151 | .154 | 84 + 85 | .141 | .144 | .146 | .149 | .151 | .154 | .156 | 85 + 86 | .144 | .146 | .149 | .151 | .154 | .156 | .159 | 86 + 87 | .146 | .149 | .151 | .154 | .157 | .159 | .162 | 87 + 88 | .149 | .151 | .154 | .157 | .159 | .162 | .165 | 88 + 89 | .151 | .154 | .156 | .159 | .162 | .165 | .167 | 89 + 90 | .153 | .156 | .159 | .162 | .164 | .167 | .170 | 90 + | | | | | | | | + 91 | .156 | .159 | .162 | .165 | .167 | .170 | .173 | 91 + 92 | .158 | .161 | .164 | .167 | .170 | .172 | .175 | 92 + 93 | .161 | .164 | .167 | .170 | .172 | .175 | .178 | 93 + 94 | .163 | .166 | .169 | .172 | .175 | .177 | .180 | 94 + 95 | .166 | .169 | .172 | .175 | .178 | .180 | .183 | 95 + 96 | .168 | .171 | .174 | .178 | .181 | .183 | .116 | 96 + 97 | .171 | .174 | .177 | .180 | .183 | .186 | .189 | 97 + 98 | .173 | .176 | .179 | .183 | .186 | .188 | .191 | 98 + 99 | .176 | .179 | .182 | .185 | .188 | .191 | .194 | 99 + 100 | .178 | .181 | .184 | .188 | .191 | .194 | .197 | 100 + ----+-------+------+-------+------+-------+------+--------+----- + + +PRINTED BY W. CLOWES AND SONS, STANFORD STREET. FOOTNOTES: + +[1] The first half of the storm, _in the case before alluded to_, is +that N.E. of the line N.W.--S.E., fig. 1, comprising the easterly and +southerly winds; and the latter half, that S.W. of the same line, +comprising the northerly and westerly winds. + +[2] This table is also applicable to the hurricanes in the neighbourhood +of Mauritius in the southern hemisphere, where all the phaenomena are +reversed; the motion of the hurricanes being towards the S.W., and the +rotation in the direction of the hands of a watch, the same barometric +and anemonal phaenomena are experienced as in a hurricane in the northern +hemisphere moving towards the N.E. + +[3] By the officer of the watch being charged with this duty, and its +being executed under his immediate superintendence, it is apprehended +that a register may be kept with great regularity. + +[4] These papers may be obtained from Messrs. W. H. Allen and Co., +Booksellers to the Honourable East India Company, No. 7, Leadenhall +Street, London. + +[5] Reports of the British Association for the Advancement of Science, +1846, p. 139. + + + + + + +End of Project Gutenberg's The Hurricane Guide, by William Radcliff Birt + +*** END OF THIS PROJECT GUTENBERG EBOOK THE HURRICANE GUIDE *** + +***** This file should be named 18534.txt or 18534.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/1/8/5/3/18534/ + +Produced by Carlos Traversi, Janet Blenkinship, and the +Online Distributed Proofreaders Europe at +http://dp.rastko.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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