A Story Outline of Evolution 



gearing is the oldest, the most extensively used and the most 

 efficient method employed in transmitting power. This is 

 accomplished by wheels containing teeth or cogs fitted on 

 shafts so that the cogs of one will fit between the cogs of the 

 other and they drive each other by pressure on the face of 

 the cogs. The speeds of rotation are governed by the size 

 of the wheels. 



Next to gear transmission, the method in most common 

 use and the one used for longer distances is that of endless 

 belts fitted on pulleys, where the power is transmitted to the 

 driven shaft by means of friction or adhesion between the 

 surface of the belt and the surface of the two pulleys. The 

 power of rope drives is accomplished in the same manner 

 while that of the chain drives is nothing more than gearing 

 by remote control. Compressed air is extensively used for 

 transmitting power where it is necessary to move the power 

 from place to place, such as in mining operations and also 

 where it is necessary to apply the power instantly. 



The discovery of a method of utilizing the power of 

 steam opened up vast avenues of other methods of produc- 

 ing power that are useful to mankind. It was discovered 

 before the coming of the steam engine that electricity could 

 be generated by friction, but power was required to furnish 

 the friction that would generate the electricity and steam 

 was the first agency to furnish this power. 



Another means of deriving power from a natural source 

 is that of the windmill, which is a motor that utilizes the 

 energy of the wind for developing power sufficient to do 

 light work. It is used more especially on farms where 

 irregular power is sufficient to meet the necessary require- 



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