PRODUCTION OF FOKCE BY COMBUSTION. 221 



attraction, or, as it is named in chemistry, a strong affinity 

 for the constituents of the combustible body, which affinity, 

 however, in most cases, can only exert itself at high tempera- 

 tures. As soon as a portion of the combustible body, for ex- 

 ample the coal, is sufficiently heated, the carbon unites itself 

 with great violence to the oxygen of the atmosphere and forms 

 a peculiar gas, carbonic acid, the same which we see foaming 

 from beer and champagne. By this combination, light and heat 

 are generated ; heat is generally developed by any combination 

 of two bodies of strong affinity for each other ; and when the 

 heat is intense enough, light appears. Hence, in the steam 

 engine, it is chemical processes and chemical forces which pro- 

 duce the astonishing work of these machines. In like manner 

 the combustion of gunpowder is a chemical process, which, 

 in the barrel of the gun, communicates living force to the 

 buUet. 



While now the steam engine develops for us mechanical 

 work out of heat, we can conversely generate heat by mechani- 

 cal forces. A skilful blacksmith can render an iron wedge red 

 hot by hammering. The axles of our carriages must be pro- 

 tected by careful greasing, from ignition through friction. 

 Even lately this property has been applied on a large scale. In 

 some factories, where a surplus of water power is at hand, this 

 surplus is applied to cause a strong iron plate to rotate swiftly 

 upon another, so that they become strongly heated by the fric- 

 tion. The heat so obtained warms the room, and thus a stove 

 without fuel is provided. Now, could not the heat generated 

 by the plates be applied to a small steam engine, which, in its 

 turn, should be able to keep the rubbing plates in motion ? 

 The perpetual motion would thus be at length found. This 

 question might be asked, and could not be decided by the 

 older mathematico-mechanical investigations. I will remark, 

 beforehand, that the general law which I will lay before you 

 answers the question in the negative. 



By a similar plan, however, a speculative American set 



