110 Trans. Acad. Sci. of St. Louis. 



order to heat an equal quantity of water 1°. Here for the 

 first time we have the equivalence of heat and work clearly 

 stated. This value was calculated from the difference be- 

 tween the two specific heats. And it is perhaps worthy of 

 remark that the direct occasion which brought about this line 

 of work, was the observation by him while in surgical prac- 

 tice in the island of Java, in 1840, that blood drawn from the 

 veins of newly arrived Europeans, possessed almost without 

 exception a surprisingly bright red color. 



At about the same time Colding in Denmark, Helmholtz in 

 Germany, Grove and Joule in England were independently 

 working upon the same subject. The work of Joule was the 

 direct determination of the mechanical equivalent of the heat 

 unit, by a method of stirring water with rotating paddles, 

 which Rumford had suggested half a century before. Row- 

 land has in our day improved on Joule's method, and has 

 undoubtedly made what is, for practical purposes, a final de- 

 termination of the mechanical equivalent of heat. Thomson 

 and Clausius completed the proof, that, while the total 

 energy of the universe is constant, a continually increasing 

 amount of this energy is becoming unavailable. Each trans- 

 formation of energy results in the production of heat, which 

 is dissipated, and so far as we can see, becomes forever un- 

 available. There is no way by which this heat can be pumped 

 back into bodies of higher temperature without a greater heat 

 loss than that which we seek to avoid. This was the final 

 proof that perpetual motion was impossible. The heat from 

 coal which drives a power-house engine is only a small part 

 of that which was liberated by the combustion under the 

 boiler. Most of this heat is wasted through the chimney, or 

 by radiation from the furnace boiler or cylinder. In convert- 

 ing the mechanical energy into a current of electricity which 

 is to be conducted to the moving car, there is a further con- 

 version into heat in the dynamo, the conducting wires and the 

 motor. When the car is stopped all the remaining energy, 

 represented by the moving car, is converted into heat at the 

 brake-shoes, and when the car comes to rest, the entire energy 

 potential in the coal has been converted into heat, which has 

 been dissipated into the colder space around. It is forever 



