186 



ELEMENTS OF GENERAL SCIENCE 



lifted. But not all of the energy which was applied to the 

 machine can be found in the weight. You may have noticed 

 in the calculation of work done upon a pulley system that 

 the work out is less than the work in. The difference between 

 the work put in and the work taken out measures the work 

 which was necessary to overcome friction and which has 



FIG. 93. The tirst automobile 



This "gas buggy" or "horseless carriage," as it was called, built by Elwood 

 Haynes, represents an early stage of one of the world's most remarkable accom- 

 plishments in mechanical use of heat energy the modern automobile 



resulted in the formation of heat. Careful studies have shown 

 that the amount of energy lost and the amount of heat produced 

 are similar. 



203. Work done by heat. Most of us have noted that a 

 steam engine, such as a railroad locomotive, must be sup- 

 plied with water and coal and that the automobile engine 

 must be supplied with gasoline (figs. 93 and 94). There are 

 some kinds of engines which are so equipped that the escaping 



