338 NINETEENTH CENTURY. FT. in. 



it would pass on into the air and we should lose sight of it ; 

 but the water is shut in and the force cannot escape, so 

 now it employs itself in dashing to and fro all the little 

 particles which make up the water, and producing the effect 

 we call heat; and as it produces exactly i Fahr. of heat 

 by the time the i Ib. weight has fallen 772 feet, we say 

 that 772 foot-pounds of force equals i Fahr. of heat. You 

 might easily prove to yourself in a somewhat unpleasant way 

 that the force is there ; for if you were to go on turning the 

 paddle violently for many hours, and there were no means 

 for the heat to escape, the motion of the particles would be 

 so violent against the sides of the boiler that it would burst. 

 Hirn's Experiments on Heat converted into Motion. 

 If you have understood this explanation, you will have 

 some idea of the theory that heat is altered motion but to 

 complete the history we require not only to turn work into 

 heat, but also to turn heat into work. This had already 

 been done many years before by a French engineer, M. 

 Carnot, though he did not understand its real significance, 

 but it has now been most beautifully proved by a long 

 series of experiments made by M. Him, of Colmar, in 

 Alsace. What M. Hirn practically did was to find out how 

 much heat can be obtained from a ton of coals, and then to 

 find out how much work was performed in an engine by 

 that amount of heat. This was by no means a simple task, 

 for much heat is lost in various ways in passing through the 

 engine ; and even when he thought he had allowed for all 

 this, it was found that some of the steam had turned back 

 into water on its way, and thus used up some of the heat. 

 At last, however, when all was carefully measured and calcu- 

 lated, he found thatj^r every pound of water heated i Fahr.> 

 enough work had been done to raise a weight of i Ib. to a 



