86' NATURE OF HEAT. 



the different properties of heat are referred to differences in 

 the size of the waves, as the differences of colour are accounted 

 for in light. Heat of the higher degrees of intensity, however, 

 admits of a kind of degradation, or conversion into heat of lower 

 intensity, to which we have nothing parallel in the case of light. 

 Thus when the calorific rays of the sun, which are of the highest 

 intensity, pass through glass, and strike a black wall, they are 

 absorbed, and appear immediately afterwards radiating from the 

 heated wall, as heat of low intensity, and are no longer capable 

 of passing through glass. It is as yet an insoluble problem to 

 reverse the order of this change, and convert heat of low into 

 heat of high intensity. We observe the same degradation of 

 heat, or loss of intensity, in condensing steam in distillation. 

 The whole heat of the steam, both latent and sensible, is trans- 

 ferred without loss in that process, to perhaps fifteen times as 

 much condensing water ; but the intensity of the heat is reduced 

 from 212o to perhaps 100 Fahr. The heat is not lost ; for the 

 fifteen parts of water at 100 are capable of melting as much ice 

 as the original steam. But by no quantity of this heat at 100 

 can temperature be raised above that degree : we have no means 

 of giving it intensity. 



If heat of low is ever changed into heat of high intensity, it 

 is in the compression of gaseous bodies by mechanical means. 

 Let steam of half the tension of the atmosphere, produced at 

 180, in a space otherwise vacuous, be reduced into half its 

 volume, by doubling the pressure upon it, and its temperature 

 will rise to 212. If the pressure be again doubled, the tempe- 

 rature will become 250, and the whole latent heat of the steam 

 will now possess that high intensity. When air itself is rapidly 

 compressed in a common syringe, we have a remarkable conver- 

 sion of heat of low into heat of very high intensity. 



It may be imagined that the elevation of temperature pro- 

 duced in the friction of hard bodies has a similar origin ; that it 

 results from the conversion of heat of low intensity, which the 

 bodies rubbed together possess, into heat of high intensity. 

 But it would be necessary further to suppose that a supply of 

 heat of low intensity to the bodies rubbed can be endlessly kept 

 up, by conduction or radiation, from contiguous bodies, as there 

 appears to be no limit to the production of heat by means of 

 friction. 



Count Rumford, by boring a cylinder of cast iron; raised the 



