178 M. '< 



forces, however unequal in magnitude, i: lade t Balance 



<>thcr simply by fixing the fulcrum so that the ratio <>f its 

 distance* fr<>in the directions of the forces shall l>c equal \ tin; 

 >e ratio of the forces. It' the fulcrum he moved from this 

 position, then that force will prej.nnderatr from which the ful- 

 crum i- ni"Ved and the c(|uilihrium will be destroyed. \\ 

 thus led to understand how mechanical al. 

 by using a crow-bar to move heavy 1. 



stone: a poker to raise the coals ii hears, 



nippers, and pincers; these last consisting of two lr\, 

 the first kind. The brake of a pump is a lever of the first 

 kind. In the Stanhope printing-press we have a remarkable 

 illustration of the mechanical advantage that can be trained 

 by levers. The frame-work in which the paj^r to !< printed 

 is fixed, is acted on by the shorter arm of a lever, the other 

 arm being connected with a second lever, the longer arm of 

 which, is worked by the pressman. These lev 

 justed that at the instant the paper comes in contact with the 

 types, the perpendiculars from the fulcra on the directions 

 of the forces acting at the shorter arms are exceedingly short, 

 and consequently the levers multiply the force exerted ly the 

 pressman to an enormous extent. 



As examples of levers of the second kind, we may m. 

 a wheelbarrow, an oar, a chipping-knife, a pair of m 



It must be observed, however, that as the lev- 

 about the fulcrum the space through which the weight is 

 moved is, in the first and second species of lever, smaller 

 than the space passed through by the power: and the 

 what is gained in power is lost in desj.atch. For example 

 in the case of the crow-bar : to raise a block of stone th 

 a given space by applying the hand at the further 

 of the lever, we must move the hand through a greater .- 

 than that which the weight describes. 



But in the third species of lever tie is the, c 



The power is nearer the fulcrum than the weight, and i 

 sequently greater; but the motion of the weight is L 

 than that of the power. In this kind of h-\ 

 gained at the expense of power. An excellent example 

 the treddle of a turning lathe. But the most strikii. 



