The Hurricane Guide Part 1

The Hurricane Guide.

by William Radcliff Birt.

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 ill.u.s.trative of the Baconian aphorism, "Knowledge is Power."

_Bethnal Green_, April 19, 1849.

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 princ.i.p.al 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 cla.s.ses 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.

[Ill.u.s.tration: Compa.s.s 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 pa.s.ses 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 pa.s.ses _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 cla.s.ses 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 lat.i.tudes than 25, the usual paths of the hurricanes are towards the north-west, in higher lat.i.tudes 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 LAt.i.tUDES.

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 pa.s.sing 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 pa.s.sing off.

HIGHER LAt.i.tUDES.

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 pa.s.sing 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 pa.s.sing 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 lat.i.tudes a storm commencing at E.N.E. pa.s.ses 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. pa.s.ses off at S.S.E. right-hand semicircle. In the higher lat.i.tudes a ship taking the storm at E.N.E. will be in the left-hand semicircle, and the hurricane will pa.s.s 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.

[Ill.u.s.tration: Fig. 2]

CHAPTER II.

PHaeNOMENA OF ATMOSPHERIC WAVES.