



f>37 



wim 



WIND. 



938 



used in a construction of this description a circumstance enhancing 

 the value of the chart ; few observations of the phenomena of cyclones, 

 as may be supposed, having been made on the land. 

 The diagram thus comprises 



I. Madras hurricane 

 II. Mauritius . . 



III. Calcutta 



IV. St. Thomas, West Indies 



Authority. 



. 1836, Observatory records. 

 . 1836, Cols. Lloyd, Lewis ; Reid. 



( 1842, II. Piddington, 7th Memoir, 

 ' I ' Jour. As. Sue.,' vol. vii. 



f 1837, Professor Dove, ill Part x. 

 " ( of * Scientific Memoirs.' 

 V. Duke of York, Kedgeree, month of ( 1833, Mr. .lames Prinsep, ' Jcur. 

 the Hooghly . . . I As. Soc.,' vol. iv., Reid, p. 291. 



VI. Havanah 1S46, ' Bermuda Royal Gazette.' 



f 1811, Observatory Reports, 5th 

 MI- Madras { Memoir, '.kur. As. Soc.,' vol. vii. 



The principle on which the diagram is constructed, is to take with- 

 out reference to the hour of the day or night at which it occurs, the 

 lowest point of the barometrical depression in a cyclone, as the centre 

 or axis of that storm. This is placed on double, or axis lines in the 

 mid He, and the fall and rise, and the time in which these occur are 

 shown on a scale of hours below, and of inches to the right and left. 

 We have thus the cyclones brought together and placed upon each 

 other, as it were, for comparison, under exactly equal conditions as to 

 time, and as to the fall of the mercury iu that time. The scale of 

 miles above will be presently explained. 



And we are immediately struck with the fact, that there are evi- 

 dently two dUtinct classes of cyclones, compared by Dove to deep 

 ravines with precipitous aides, and to extensive valleys with gentle 

 declivities, in one of which the fall and rise arv more ur less gradual, 

 forming an easy curve, while in the others it forms not so much a 

 curve but almost an angle, or rather the figures called by opticians 

 caustic curves, and in these last cyclones the fall has been excessive 

 and the fury of the tempest far beyond the average of such visitations. 

 We may thus divide the storms into a first and second class ; the first 

 class being those of the greatest (excessive), and sudden falls near the 

 centre. 



There ia also evidently another peculiarity, that ia, that all the rapid 

 part of the fall seems to begin at from three to six hours before the 

 passage of the centre, and that before that time the fall even of the 

 violent cyclones is comparatively gradual, and in fact approaches closely 

 to the second class. 



The scale which Mr. Piddingtoi), after much consideration, found 



irest to the probable truth, is that marked in miles on the upper 



part ni thi: diagram, though this is to be considered as by no mrans 



fctrictly a limit ; for, as regards limits, he says it may possibly be found 



in' the end that there are no strict ones at all, and that even the various 



extremes may be wider apart than the following table will indicate : 



An average fall of the barometer Shows the distance of the centre 



per hour of 

 From . To. 



0-020 . . . 0-OCO 

 0-060 . . . 0-080 

 0-080 . . 0-120 

 0-120 . . . 0-150 



from the ship to be in milci*, 



From. To. 



250 . . . 150 



150 .. . 100 



100 . . . 80 



80 . . .50 



The third decimal of the barometer heights ia replaced by a cypher. 



" I have not set down anything," Sir. Piddington remarks, in con- 

 tinuation, " for the centre division of our table, that is, from the centre 

 to 3A before its passage, for it will be seen that the rate of fall per 

 hour doubles after the cyclone has fairly begun and lasted six hours ; 

 and that then (from 3A to II, or from nine hours after the commence- 

 ment up to the centre) it may either continue to fall at the same rate 

 of about O'l per hour, or a little more, or that its rate of fall per hour 

 may be, if it should be a cyclone of the first class, as 100 to 400, when 

 compared with that of the former three hours ; or, in other words, 

 that it will now begin tu fall four times as fast, or 0'40 per hour ! 

 \\ i .ivc plenty of instances of tliU, and even of a fall of more than <r5 

 i (half or three-quarters of an inch) in the hour ! I doubt not 

 that this peculiarity will fully account to the seaman for, and I hope 

 put him well on his guard against, cases of sudden falls, which, if 

 they occur at the beginning of cyclones, as they sometimes do, are 

 warning enough, of course ; but which may aluo advise him of his too 

 near approach to danger of such imminence that we may at least say 

 that no ship can hope to escape from it with her masts standing ; and 

 ho should in such cases have the axes upon deck- a precaution too often 

 neglected by young commanders and officers, who are apt to suppose 

 that caution indicates fear, and they are sometimes afraid of being 

 thought afraid of the storm. It will be remembered, also, that it is 

 quite impossible by any previous rates of fall to estimate, when so near 

 the centre, which of the classes of storms we have to deal with ; and I 

 repeat that what we have to do with our ship must all be done before 

 this time." 



Below the framing-line, at the bottom of the diagram, is represented 

 in section, on a very small scale, the entire form of cyclones, as from 

 Mr. 1'iddington's discussion of his own and other results it would 

 appear to be a disc, the thicknens or height of which measures a very 

 auiall fraction only of its diameter. The lines indicate the discs of 



cyclones of 300 miles in diameter, and of 10, 7, and 3 miles in height 

 respectively, with a supposed vortex (*) at the centre, which has ;v 

 calm of 10 miles at its base. " The reader," Mr. Piddington remarks, 

 " may from this estimate what it would be if 5 or even 15 miles high, 

 and how fallacious all our notions are apt to become when we consider 

 these storms as whirling columns, and insensibly go on to liken them 

 to waterspouts as to height, which it is evident they cannot at all 

 resemble, since their size (diameter) may be said to have been in many 

 cases estimated to a few miles with tolerable correctness ; and iu 

 frequent instances the next stratum of clouds above the storm, either 

 at rest or moving altogether di6'erent!y, has also been clearly distin- 

 guished and noted : so that we may boldly affirm that at most the 

 height (thickness is the more correct word) of the disc never exceeds 

 10 miles, and usually falls far short of it." The cyclone-disc, indeed, 

 is sometimes so thin, that at or near the centre, whether calm or not, 

 it has often been seen through, of which the following, iu Mr. Piddiug- 

 ton's opinion, are instances : Dr. Malcomsou, in describing a cyclone 

 in the Arabian Sea, in which a ship was dismasted and iu great clanger, 

 after alluding to the intensely dark masses of clouds that pressed down, 

 as it were, on the troubled sea, states that, " In the zenith there was 

 visibly an obscure circle of imperfect light of 10 or 12 degrees." In 

 another storm, which was a true cyclone by its veering, and a tornado 

 as to duration and violence, while all round the horizon was a thick 

 dark bank of clouds, the sky above was so perfectly clear that the stars 

 were seen. In the cyclone, one of the number investigated by Mr. 

 Piddington, of October, 1849, in the Bay of Bengal, at the time of the 

 passage of the centre over the lighthouse at False Point, Pahniras, or 

 for about two hours of calm, the stars were seen very clear overhead, 

 with a thick bank of haze all round. In this instance, also, the 

 observers in several ships speak of a circle of light, or of its being much 

 clearer overhead at the centre; "and this is exactly the appearance 

 which should occur to an observer situated at the centre of a thin disc, 

 as well as to one in the focus of a thick vortex." The phenomenon, iu 

 fact, is so constant, as to have received a name from the Spanish 

 navigators, who call it " the eye of the storm." 



We proceed to explain some popular designations connected with 

 the subject, and the phenomena to which they more specifically 

 relate : 



T'irnadn, a whirlwind, from the Spanish tornar, to turn, is the 

 term given to a sudden and violent cyclonal storm, accompanied by 

 lightning and thunder and heavy torrents of rain, as observed origin- 

 ally on the coast of Africa, and iu the Spanish West Indies. Terrestrial 

 bodies within its influence are violently displaced, or the ocean is 

 strongly agitated : on laud, forests, plantations, and buildings are 

 destroyed ; and at sea, ships are engulfed' or driven on shore : the 

 effects are of course the greatest near the circumference of the vortex, 

 and the space within which they are felt varies in extent; sometimes 

 the diameter of the area is several miles, and at other times it does 

 not exceed one hundred yards. The approach of the btorrn is fore- 

 boded in the morning by the appearance, over the land, of dark 

 clouds which move towards the sea, while a gentle breeze is blow- 

 ing towards the shore: soon afterwards the rain conies down in 

 torrents, and the lightning darting from the clouds resembles showers 

 of electric matter. While the tornado is passing over a ship, which may 

 be four or five hours from the first appearance of the clouds, the ikuhes 

 cease, but the rain continues, and a loud crackling noise, occasioned by 

 the electric fluid descending along the masts, is distinctly heard 

 among the rigging. After the squall has passed beyond the ship, 

 the lightnings again appear to descend in sheets as they did on its 

 approach. 



A less extensive whirlwind is frequently preceded by a remarkable 

 tranquillity of the atmosphere and a sultry heat; when suddenly, 

 within a circle of one or two hundred yards only in diameter, a 

 revolving motion of the air commences, and is accompanied by thunder 

 and rain : the velocity of the rotatiou gradually increases, and at 

 length its violence is such as to tear up trees and destroy buildings 

 which may be within the vortex. It may not continue longer than 

 j half an hour, but in that short time the damage is immense, and the 

 loss of life is frequently considerable. 



Tfffhouu (Greek Tvquv, a whirlwind) is a name frequently applied 

 to a tropical storm : it is also giveu to the hot winds which occasionally 

 blow with great violence in Africa, Syria, Arabia, and Persia ; and 

 which are felt, though rarely and with much-diminished force, in the 

 southern parts of Italy and Spain. It has been supposed that tho 

 Chinese designation for a cyclone, Tfiju-m, was also originally derived 

 from the Greek, but Mr. I'iddingtou has shown, after the celebrated 

 sinologist Dr. Morrison, that it is indubitably a Chinese word. Tho 

 latter relates that there are in China " temples dedicated to the 

 Tyfoon, the god (goddess ? ) of which they call A'CK woo, ' the tyfoon 

 mother," in allusion to its producing a gale from every point of the 

 compass, and this mother-gale, with her numerous offspring, or a union 

 of gales from the four quarters of heaven, make conjointly a tarfuny, 

 or tyfoon." The sirocco of Egypt and the coasts of the Mediterranean. 

 the simoom of Arabia, and the harmattan of the coast of Guinea, are 

 understood to be so many designations of the typhoon ; all of them 

 being supposed to originate in the same cause. 



Frequently when the winds have a whirling as well as a progressive 

 motion, columns of sand are raised and driven about with great 



