WIXD. 



W1XD. 



outh-ract : and in Colonel Capper's work on the ' Winds and Mod- 

 Don*,' which wu published in 1801, the gyratory nature of the storms 

 ! the Rut Indian seas it inferred froui the recorded change* in the 

 diraotioaaof the wind during the storms of 1760 and 177". Whirl 

 wind itormt appear however to hare been then considered u local and 

 temporary ; and we owe to the late Mr. Uedfield, of New York, the 

 discovery that they hare a progressive a> well as a revolving motion. 

 Dr. Knnklin ascertained that the atorm which he witnessed at Phila 

 delphia in 1743, took a certain time to arrive at Boeton, but he did 

 not ponue the mibjeot, and, from a mistaken estimate of the distance 

 between those cities, his opinion of the rate of movement is now known 



: . : .- 



Currents of air are frequently, as at the change* of the monsoons in 

 the East Indian seas, impelled obliquely against each other, and tlm- 

 rotatory motions in the atmosphere may 1* produced, exactly as eddies 

 or whirlpools are formed in currents of water. [WHIRLPOOL.] 



Mr. Redfield, in his ' Observations on Storms,' in the ' Transactions 

 of the American Philosophical Society,' 1841, offers an opinion that 

 generally during a gale there is, in the lower part of the atmosphere, a 

 spiral motion inclining downwards and towards the centre ; and in the 

 higher regions a like spiral motion inclining upwards and towards the 

 exterior. He adds that, in storms of great extent, there is sometimes 

 found a considerable area within which the winds are moderate and 

 blow in various directions. These characters of a revolving storm 

 appear to be verified by the manner in which trees were prostrated 

 during the hurricane which occurred in New Brunswick in June, 

 1885; when, about the centre, bodies of great weight were carried 

 spirally upwards, and, on opposite sides of the storm's path, the trees 

 were thrown in contrary directions. It is observed that when :. 

 storm rages violently, the doom and windows of houses are often 

 forced outwards, either from the centrifugal force caused by the 

 revolving motion, or from the expansion of the air within, when a 

 temporary rarefaction takes place on the exterior ; and from the move- 

 ments of the clouds it appear* often that a storm, in passing over a 

 place, is in activity at a considerable altitude before it descends to the 

 earth's surface. 



That a whirlwind may have a progressive as well as a revolving 

 motion may be easily understood if it be observed that, as the atmos- 

 phere in the tropical regions moves from east to west with respect to 

 the surface of the land or sea, it may, after crossing the Atlantic and 

 Pacific oceans, be arrested in its progress westward by the continents 

 of America and Asia, and deflected from thence towards the poles : 

 the whirlwinds formed by electricity or otherwise in the general 

 current of air will consequently be carried with the deflected branches 

 into high northern and southern latitudes; and it may occasionally 

 happen that, from the nature of the deflecting forces, the path of the 

 axis of a revolving storm in either branch U a curve line like a segment 

 of a circle or a parabola. Sir John K. W. Herschel, at the meeting of 

 the British Association in 1838, suggested that the Gulf-Stream may 

 be the cause of the nearly parabolic curves assumed by the paths of 

 the storms on the coast of North America : the paths nearly coincide 

 with the course of this stream ; and the warmth of the water, by 

 increasing the temperature of the air above it, must disturb the 

 equilibrium of the atmosphere, and maintain the storms which had 

 their origin in a lower latitude. 



It i evident that the velocity of the wind in a revolving storm must 

 be the greatest and the least respectively on opposite sides of the axis 

 of rotation, in a diameter which is perpendicular to the path of that 

 axis ; for on one side the direction of the revolving cur rent conspires with 

 that of the progressive motion of the storm, and on the other it is con- 

 trary to it. In other parts within the limits of the storm the direction 

 and velocity of the wind must bo compounded of the rotative and 

 progressive motions; and it will happen frequently that a temporary 

 calm is experienced at each point on the earth's surface at which the 

 axis of the storm successively arrives. 



The phenomena of tropical storms are not precisely such as they 

 would be if the air had a simple movement of rotation ; the particles of 

 air, while revolving, ore probably subject to undulatory motion* in 

 spiral run-en, ami the wind appears sometimes to shift to d 

 point* all round the coni]>ass. Mr. Itedlield states that, in small whirl- 

 winds, the axis of rotation appears at times to describe gyrations in 

 looped curves about its mean place in the line of progressive motion ; 

 and the like gyrations probably take place in those of an extensive 

 kind ; indeed in some voyages under the influence of revolving 

 they have been actually observed : but in order to simplify th< 

 nation of the phenomena of whirlwinds, it is usual to assume that the 

 particles of air revolve in the circumferences of circles whose centres 

 are in the axis ; the Utter having at the same time a movement of 

 progression in a rectilinear or curvilinear direction. Now, if the 

 plane of the paper represent the surface of the sen, anil a line t! 

 A,, perpendicular to it, represent the axis of a whirlwind whose north 

 and south diameter i- V. S , :.n.| in which the particles of air are sup- 

 posed to revolve (for example) in the ilin'<'ti<>n indicated by the onler 

 of the letters N., W., S., K. ; the progressive movement of the axis being 

 also supposed to be from A, through X . or from south to north: then, 

 since at N. a tangent to the circle lies due east and wost, it is 

 that a ship at that point would experience a wind blowing from the 

 cart when the centre of the storm is at A, ; and if the ship remain 



stationary, the wind will continue to blow from the same quarter 

 till A, arrives at N., the tangents to the concent :k circle* i. 

 to be described by the particles being due east and wiut at the 

 northern point* of the circumferences u they successively am vv at 

 N., and the wind in all the northern half of the storm revoK 

 the direction !'.. N., W. : but after this time, the wind blowing i 



direction AV., S., K., must be felt at N. as a* west wiud till the-re'i 

 half of the storm has passed over that point. In li if the 



axis of the storm were to move, from A, towards W., a ship supposed 

 to be stationary at the latter point would feel the gale from th. 

 till A I arrives at W. ; after which, as the eastern semicircle pa&sv 

 that point, the ship would experience a wind from the south. 



Again, if the axis were to move from A, towards A., tli.U is. from 

 south-west to north-east, for example, the direction of tin whirlwind 

 licing, as before, according to the order of the letters N., N 

 the ship being supposed to remain stationary at no: M. till 



the storm has passed over it, then the line of direction in which the 

 points of the whirlwind successively overtake the ship being 

 parallel to A, A s , the arcs nil,, In,, lie., will represent the 

 directions in which the wind will successively be felt luring 



the continuance of the sin-in. Thus, the axis of the whirlwind 

 at A,, the convex surface of the storm h.-is just re.n-hed the sh! 

 the wind blows in the direction a M,, or in the circumference of the 

 circle whose centre is A,, that is, nearly from the east south-east ; 

 next, the axis being at A t , the point kl, in t! 

 cmlc whose radius is A, ,, U at u, ; and then, at the ship the 

 felt in the direction ill,, or in the circumference whose radius is A, u,, 

 or its equal A, M,, that is, nearly from the east-by-south. Again, tin- 

 axis being at A,, the point M, in the circumference whose radius is A, M,, 

 is at M, ; and then at the ship the wiud is felt in the direction CM,, or 

 in the circumference whose radius is A s M,, or its equal \ 

 from the north-east. When the axis is at A, and A S the points 11, and 

 M 5 arrive at M,, and the wind there is felt successively in t ! . 

 rfsi, and CM,, that is, nearly from the north i>\ irMt, .-md from the 

 north-north-west. When the axis has advanced beyond A,, it is evident 

 that the whirlwind ceases to i ifect on a ship at M,. If t.m 



gents were drawn at .M, to the ores ill,, CM,, &e... they would c\ 

 be parallel to tangents at tic iing points M,, M 3 , ic. ; there- 



fore the directions in which the circumference of the concentric . 

 meet the line of direction M, M, will be those in which the win I 

 at the ship during the storm. In like manner, the successive 



v.hi.-!i the wind blows in a revolving storm may i 



whatever bo the situation of the ship and tho movement of the axis of 

 rotation. 



The diagram, therefore, may be regarded as a plan or a lioi > 

 section, or, more accurately, a section at right angles t > t i 

 revolving storm. In the sequel of tl> w-ill lie 



found, presenting vertical sections of such 

 to their axis, and at right angles to their greatest diameter. 



The hurricanes or w hii Iwinds of the At 

 the ocean which is frequently designated the region of \ .., 

 ami U situated between 10* and 20' N. lat , and o, 



. anil their progress along the coast of the United States is 

 marked by the devastation t They are fell 



between .Inly and October, but they are i ut and violent in 



August and Scptomlier ; and living <> the great line of con 

 between Kui..pc and the West, the phenomena wl. 

 have been more attentively observed than th ae of the M 

 other region of the earth. The valuable publication i Mr. !: 

 contain nearly all the details which have yet been collected concerning 





