DYNAMOMETER FOR ROTARY MOTION. 107 



When the fly-wheel is turned in the direction shown by 

 the arrow, it causes the two cog-wheels to revolve, and 

 moves the band in the direction shown by the other arrow. 

 Now, whatever force is required to turn the wheel /*, con- 

 nected with the machine under trial, must be overcome by 

 a corresponding force applied to the handle , because 

 the wheel-work is so adjusted that this handle moves with 

 the same velocity as the band on the band-wheels. 



The Avlieel /", being connected by the band to the wheel 

 c?, which is on the same axis or shaft as the cog-wheel /, 

 the resistance of the machine under trial tends to keep 

 the cog-wheel I from turning, until enough force is ap- 

 plied to the handle , to set the cog-wheel Jc in motion. 

 Now the greater the resistance, the greater will be the 

 power needed at the handle. This power, therefore, is 

 measured accurately in the following manner : 



The axle g^ of the cog-wheel I, rests at its further end 

 in an oblong hole or mortise, which 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 lever 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 I to refuse to turn ; consequently, 

 his force, instead of turning it, lifts it up in the mortise, 

 and raises the lever with it. As he increases 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 needed 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 I, while the machine is at rest, or before 



