HOW WORK IS DONE 



OTHER MEANS OF TRANSMITTING POWER 



Power is transmitted directly from one part of a 

 machine to another, in the case of a great variety of 

 machines, with the aid of cogged gearing wheels of 

 various sizes. The modifications of detail in the appli- 

 cation of these wheels may be almost infinite, but the 

 principle involved is always the same. The case of two 

 wheels toothed about the circumference, the teeth of 

 the two wheels fitting into one another, illustrates the 

 principle involved. A consideration of the mechanism 

 will show that here we have virtually a lever fixed at 

 both ends, represented by the radii of the two wheels, 

 the power being applied through the axle of one wheel, 

 and the weight, for purposes of calculation, being rep- 

 resented by the pressure of the teeth of one wheel upon 

 those of the other. So this becomes a lever of the 

 second class, and the relations of power between the 

 two wheels are easily calculated from the relative 

 lengths of the radii. If, for example, one radius is 

 twice as long as the other, the transmission of power 

 will be, obviously, in the proportion of two to one, and 

 meantime the distance traversed by the circumference 

 of one wheel will be twice as great as that traversed by 

 the other. 



A modification of the toothed wheel is furnished by 

 wheels which may be separated by a considerable dis- 

 tance, and the circumferences of which are connected 

 by a belt or by a chain. The principle of action here 

 is precisely the same, the belt or chain serving merely 

 as a means of lengthening out our lever. The relative 



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