WHE 



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sometimes by handspikes, as in the 

 capstan; sometimes by handles, as in 

 the windlass. 



WHEEL-CUTTING. A term applied 

 to a particular branch of practical me- 

 chanics, which comprehends the modes 

 of cutting the teeth in the wheels used 

 by watch and clock-makers, and for other 

 mechanical purposes. 



WHEEL, EXCENTRIC. An appa- 

 ratus employed in double-acting steam- 

 engines, for the purpose of opening and 

 closing the valves of the cylinder. On 

 the shaft or axis of the fly-wheel, or 

 of the paddle-wheel, is fixed a wheel 

 which revolves with it, but whose motion 

 is excentric to it — that is, the centre of 

 the wheel does not coincide with the 

 centre of the shaft or axis ; and, hence, 

 the centre of the wheel moves round the 

 axis of the shaft. The distance of the 

 centre of the wheel from that of the shaft 

 constitutes the amount of excentricity, 

 and this amount is equal to one half of 

 the range of motion of the valves which 

 are to be worked by this mechanism. 



WHEEL, PADDLE. A wheel placed 

 at each extremity of the shaft of a marine 

 steam-engine, for the purpose of pro- 

 pelling the vessel by its revolution. It 

 may be considered as a series of levert, 

 arranged in a circle, and brought suc- 

 cessively into action ; the fulcrum is ob- 

 tained by the re-action of the water upon 

 the paddles ; the resistance to be over- 

 come is that of the water opposed to the 

 progress of the vessel, and acting on the 

 centre of the wheel ; the power by which 

 the resistance is to be overcome, is ap- 

 plied by the cranks of the engine upon 

 the shaft which connects the centres of 

 the wheels. 



WHEEL, RATCHET. Awheel em- 

 ployed for preventing motion in one 

 direction, while it permits it in another. 

 To effect this object, the teeth of the 

 wheel are cut with their faces inclining 

 in one direction, and a small lever or 

 catch is so placed, as to enter the inden- 

 tation and stop the wheel if it turn back- 

 wards, but slides over the teeth without 

 obstructing them, if it move forward. 

 Such a wheel is generally employed to 

 prevent a weight raised by a machine 

 from descending, and to obviate other 

 retrograde movements. 



WHEEL, SPUR, CROWN, BE- 

 VELLED. These are designations of 

 toothed wheels, and denote the position 

 of the teeth relatively to the axis. In 

 the spur wheel, the teeth are raised upon 

 377 



the edge of the wheel, or are perpen- 

 dicular to the axis ; in the crovm wheel, 

 the teeth are parallel to ^he axis, or per- 

 pendicular to the plane of the wheel ; in 

 the bevelled wheel, the teeth are raised on 

 a surface inclined to the plane of the 

 wheel. 



WHEEL, SUN AND PLANET. A 

 contrivance for converting the alternating 

 motion of the beam of a steam-engine 

 into a rotatory motion. In this appa- 

 ratus a toothed wheel is fixed upon the 

 axis to be turned, and another wheel, 

 gearing with it, is attached to the lower 

 end of the connecting rod, so that it can- 

 not revolve on its own axis. The result of 

 this arrangement is that the second, or 

 planet-wheel, passes completely round the 

 first during each up and down stroke of 

 the engine, and, in so doing, causes the 

 first, or sun-wheel, to rotate upon its axis. 

 This apparatus has been superseded by 

 the crank. 



WHEEL, UNDERSHOT. A water- 

 wheel, in which the water strikes the 

 float-boards below the axle, and acts by 

 the impulse due to its velocity. See 

 Overshot wheel. 



WHET SLATE. Whetstone-slate. A 

 variety of slate, occurring in beds in pri- 

 mitive and transition clay-slate. Very 

 fine specimens are brought from Turkey, 

 under the name of hone-stones. 



WHINSTONE. A provincial term 

 applied to some of the trap rocks. 



WHIRLPOOL OR EDDY. The phe- 

 nomenon which occurs when two oppo- 

 site currents of the ocean meet one an- 

 other, turn upon a centre, and assume a 

 spiral form. The most celebrated whirl- 

 pools are those of the Euripus, the Cha- 

 rybdis, and the Maelstrom. 



WHIRLWIND. A spiral or whirling 

 motion of the wind, which occurs when 

 its direction is influenced by the form of 

 precipitous mountains, or when two 

 winds meet each other at an angle, and 

 then turn upon a centre. In the deserts 

 of Africa, they sometimes draw up the 

 sand into a moving pillar, which buries 

 all in its way. When they occur on the 

 ocean, they draw up the water, and pro- 

 duce water-spouts. 



WHISPERING GALLERY. A dome 

 or room so constructed that words uttered 

 in a low tone at one spot are audible at 

 some other spot, while persons standing 

 between these two points cannot hear 

 what is said. To produce this effect, the 

 room should have an oval or elliptical 

 form, so that words spoken in one focus 



