\\IN( H AND AXLK. 





-i 



iMMinr The machine it used to nice a weight vertically, or to draw 

 MI object toward* it ; for which purpoMt the object is connected with 

 it by a rope or chain which continually passes over the curve surface 

 of the cylinder aa the latter u made to turn on its axis by a man 

 acting at the handle. Since the cylinder revolve* once v 

 handle, or the extremity of the lever to which it is atta< 

 made to describe the circumference of a circle, it 11 evident that the 

 mechanical power of the machine u precisely that of the wheel and 

 axle. [WHUI. AND AXLE.] When of a simple form it it ei 

 to raise water from a well, and earth or some other material from tho 

 shaft of a amall mine : and one of a complex nature is used, by means 

 uf a crane, to raiae qaska or heavy packages from the ground, to the 

 upper part of a building. 



When great weight* are to be raised, the machine in usually fixed 

 in a frame of cast-iron, which La rectangular on the plan, but its extre- 

 mities or faces have the form of a triangle, or of the letter A. The 

 axle of the cylinder U supported on a horizontal bar at the middle of 

 each end of the frame, and to the cylinder is attached a toothed-wheel 

 which turns with it on the common axis : above this wheel and 

 parallel to the cylinder is an iron axle which carries a pinion with 

 teeth working in those of the wheel, and causing the latter to 

 revolve, the pinion itself being turned by means of the lever and 

 handle at one or at each extremity of the frame. A machine of 

 this kind is called a crab ; and when a weight is to be drawn horizon- 

 tally, or raised above the cylinder, the machine must of course be 

 bolted to the floor or firmly fixed in the ground, in order to prevent it 

 from being moved from its place. In such machines there is generally, 

 at one extremity of the cylinder a wheel, having on its circumference 

 teeth like those of a saw ; and a did- or catch, which turns freely on 

 a pin, is attached by that pin to the side of the frame in such a 

 manner that it may fall between the teeth. By this contrivance, if 

 the handle should break, or the moving power be taken oil while 

 the weight U suspended in the air, the latter is prevented from 

 . - 



Machines of this kind are occasionally constructed which have the 

 ]iower of holding the weight in any part of its ascent or descent with- 

 out a ratchet-wheel and catch. Such a machine consists of a barrel 

 formed in two cylindrical portions, A and B, of different diameters, but 

 having a common axle : the rope passes under a pulley in the block c, 

 to which the weight is attached, and over the two cylinders, in such a 

 manner that when the handle is turned it uncoils from the smaller and 

 coils upon the larger portion. Thus every revolution of the barrel causes 

 the larger cylinder to take up a quantity of rope equal in length to its 

 circumference, while there is uncoiled from the smaller a quantity equal 

 to the circumference of the latter: consequently, after each revolution, 

 the quanti"; 'ween the axis of the cylinder and tin- pulley is 



diminished by the difference between the two circumferences, and the 

 weight is raised up through a height equal to half that din 

 Hence by mechanics, if 2H represent the circumference of the 

 circle described by the handle of tl,.- \\n\.\\ in nne revolution. 

 (r f r)w half the difference between the circumferences of the two 

 cylinders, w the weight to be raised, and r the power applied to the 



handle, we shall have, in the state of equilibrium, -5 w = r. 



The weight which may be balanced by a given power r will 



tly be greater a* r' r, or the difference between the radii of the 



cylinder, is lew ; and the difference may be made very small with' nit 



inn' h increasing the friction. The only disadvantage attending the 



ne, when compared with an ordinary winch or capstan, is that 



it "|<imv a much greater quantity of rope to raise or move the object 



through any given distance. It wan Brut proponed in Kurope by Mr. 



George Eckhardt, but machines of a like kind have, it is said, been 



long in line in the East. 



The winch i* employed with the common jaek. which in used to lift 

 great weights, or to move them through small distances. The handle 

 turn* a pinion with teeth, which act cm others at the circumference of a 

 small wheel; and on the axle yf thw w a pinion with teeth which work in 



those of a rack-rod. The axle* of the wheel and pinions being let into the 

 aide* of a case of wood or iron, the revolution of the wheel produce* a 

 rectilinear motion of the rack ; and one end of the case being fixed to 

 the ground, or against an immoveable object, the extremity of the rack 

 at the opposite end forces forward the body which is to be displaced. 



nies, instead of a rack, the machine is fumUhed with a 

 whose axle is hollow, and cut in the form of a concave screw ; within 

 this screw is one of the convex kiud, which by the r. volution of ti.- 

 wheel and its axle is made to move in tl. 

 thus to press before it the object which ia to be i 

 has however considerable friction. 



The force exerted by a man in turning a winch vertically vanes 

 according to the jiosition of the lever with respect to the I. 

 When the lever, or that part which is perpendicular to the axle, 

 lar to the ground, and the handle is at the highest or 

 part of the circle described by the end of the lever, the man 

 pushes the handle directly from him, or pulls it directly toward* 

 him ; and in each case he exerts a power which is estimated 

 at -27 or 30 Ibs. ; but when the lever is in a horizontal posi- 

 tion, tho man either throws a great portion of his weight on 

 the handle to press it down, or he exerts his muscular force in a 

 direct manner to pull it upwards; and the force exerted in these 

 positions is estimated at 140 or 160 Ibs. The force exerted must 

 evidently have different values between these quantities in other posi- 

 tions of the winch : and the practice is to cause two men 

 the same time to turn the machine, one being at each extremity of the 

 axle of the cylinder. The levers of the two winches are placed at 

 right angles to one another ; consequently when one man is pushing or 

 pulling horizontally, the other is pressing or pulling vertically, an. I thus 

 the operation of turning goes on with nearly uniform intensity ; the 

 first man working in the least favourable position when the other ix 

 working iu that which is most so. [WINDLASS-.] 



WIND is a motion of the atmosphere independent of that whirh it 

 has in consequence of the diurnal and annual movements of the earth. 

 The latter motion being performed in a part of space which may be 

 considered as devoid of any resisting medium, the particles of air .-nili-i- 

 no partial displacements on that account; and the friction of tho 

 particles against each other, and against the earth which tl. 

 round, must have long since brought the diurnal movci 

 atmosphere and earth to a state of equality : thus, the am-' 

 of the air on any parallel of terrestrial latitude being the same as that 

 of an observer on the same parallel, the air would seem to be at rest 

 about him. But if, from any disturbance of the equilibrium of the 

 atmosphere, the particles should move less rapidly than the observer 

 from west to east, or should acquire movements in some other direction, 

 then the sensation of a wind would be experienced. The tides which 

 take place in the atmosphere by the attractions of the sun, moon, and 

 planets on the particles of air giving rise to differences in the ' 

 of the vertical columns, they must necessarily cause inequalities of 

 pressure in horizontal directions, and thus produce winds or currents 

 of air ; but it has been shown by La Place that these currents are 

 scarcely sensible ; and such attractions are by no means adequate to 

 the production of the winds which are observed on the earth's >- 

 [ATMosruEiiE, col. 092.] 



The immediate effect of the solar radiation, communicating 1> 

 any region of the earth's surface, is to generate an ascen 

 ment iu the incumbent atmosphere, a bodily overflowing of its ir 

 above, and a relief of barometrical 1 pressure below. The air of the 

 cooler surrounding region, not being so relieved, will be driver 

 the difference of hydrostatic in this case of atmospheric pi 

 so arising, and thus originate two distinct winds : an upper one . 

 outward from the heated region; a lower iuward, or towards it, If 

 the region heated be a limited one, these currents will radial 

 and to it as a centre ; if a linear belt, or a whole zone of the globe 

 intervene, such as the generally heated intertropical region, they will 

 assume the character of two sheets of air sotting inwards on both sides 

 below, uniting and flowing vertically upwards along the medial line, 

 and again separating aloft and taking on a reversed n 



These effects of heat upon the atmosphere, together with the rotatory 

 motion of the earth, are the primary causes of all the phenori: 

 the winds, the latter having lie. u found liy modern meteorolo;. 

 have a much more extensive influence than was supposed when its part 

 in the production of the trade-winds was first duly recopni-i '1. On 

 this account, and because the consequences of these ui. 

 impart to us a key to tho whole subject, including even that \ 

 it which relates to revolving storms, or cyclones, we shall now pro- 

 ceed to consider the trade-winds, both with ret j 

 to their facts, in some adequate detail. 



' is the term used by seamen to indicate the pei 

 or constant winds, l>ecaiiso they promote more tlian mini 



stance navigation and trade. These perpetual or trade indh occur in 

 all open Hc:ut on IH.UI xidex of the e.jiiator, and i 

 30 degrees north and south of it. They were not known to t 

 and seem to have l>cen unkno u seamen nptoti. 



f Columbus. Th' i:uo Portuguese navigatora I. .-..1 pro- 



ceeded a* far as the Cap< 



great distance from the coast of Africa, and consequently t 

 entered the regions where the trade-winds Mow. Cohiml 



