-VI.] 



MECHANICS. 



S3 





application of the principle of the 

 .le. 



::st'in is. perhaps, the most 



^ and only differs from 



udUss in having its revolving axis 



Ftg.M. 



placed vertically. The circumference is 

 pierced with holes, which receive long 

 levers, by which it is worked by men, who 

 walk round the capstan, and make it re- 

 volve by pressing the ends of the levers 

 forward "l-mill IB another variety. 



In this case the weight of several people 

 . on the circumference of a long 

 - it to revolve. The paddle- 

 f a tteam-boat arts on the sam'- prin- 

 the water, which offers a res 

 to the motion of the paddle-board- 

 power. 



> >e it not sometimes happen 

 that these machines will stop for a short 



to recoil ? 



Ye ; hut. in order to previ nt the 

 rrcoil, it is UMI.I! to have a wheel, 



whffl. fixed to the axle 

 to as to allow it to turn in one ciir 



prevent it going back, 

 x a catch placed at the aide, which 

 falls into the space between the teeth, and 

 prevents the 



7*. If we make a wheel larger in 

 circumference, what will be the effect? 



It will lengthen the long arm of 

 the lever, consequently we shni 



weight 

 axle. 



/'. If ihi bo the case, do we not 



itn ? 

 /*.- a a little as 



Advantage i 

 but then we lose it again, because the 



power has to descend through a propor- 

 tionably greater space, in order to rai-e the 

 through the same space in the same 

 amount of time. 



82. T. Can you tell me how the very 

 great inconvenience of having a large 

 wheel on a very slender axle may be avoided, 

 without diminishing the mechanical ad- 

 vantage? 



P. Yes ; by employing a machine, 

 which is called the Chinese wheel and axle, 

 because it was introduced into this country 

 from China. It consists of two cylinders, 



Fif. JU 



one larger than the other, turning about the 

 \is. The weight is attached to a 

 pulley, which plays on a long cord, which 

 is coiled round both axles in contrary 

 ciirecti 'lie winch is turned, one 



end of the eord uncoils from the smaller 

 cylinder, and is wound round tlv ! 

 thus the weight is <-le\ ; turn, 



through a space equal to half of the differ- 

 ence between file circumt'errnrr of the 



: 



. witli its ]n. c ratio 



half its excess above that of the lesser one. 



\L QUEST 



1 ' 



> ihriraxles? 

 is the machine been son 



pluin how a wheel and axle re- 

 'i*rr of a wheel' 



.ve all wheel* central 

 7. Where is the fulor. 

 placed ! 



