128 MECHANICS. 



power, therefore, is measured accurately in the follow- 

 ing manner : 



The axle, g; of the cog-wheel, /, rests at its further 

 end in an oblong hole or mortise, that allows it liberty 

 to play, or rattle up and down within narrow limits. 

 This same axle, g, passes through a hole in the lever, 

 i, so that when it rattles up and down, it carries this 

 lever up and down with it. The other part of the lev- 

 er turns on the shaft, h, of the other cog-wheel. 



Now when the man at the fly-wheel applies his 

 force to the handle, a, the resistance of the machine 

 under trial causes the cog-wheel, /, to refuse to turn ; 

 consequently, his force, instead of turning it, hfts it up 

 in the mortise, and raises the lever with it. As he in- 

 creases his force against the handle, let weights be 

 hung on the lever, until, at the very moment that the 

 wheel begins to revolve, the weights shall be just heavy 

 enough to keep the lever down in the mortise. This 

 weight, therefore, will measure the exact force need- 

 ed to turn the machine : the greater the resistance of 

 the machine, the greater must be the weight. 



There is another weight, J, used to balance the 

 lever and cog-wheel, /, while the machine is at rest, or 

 before the force is applied to it, so that the weight at 

 m shall represent the force truly. The weight, m, is, 

 of course, to be multipUed by the power it exerts on 

 the lever, i, which should be graduated like the bar of 

 a steelyard. 



There are a few other parts of this dynamometer not 

 yet described. One is the cyHnder, o, filled with oil, 

 in which a perforated piston works, preventing the 

 rapid vibration of the lever, i, as the force varies, pre- 



