HEAT. 77 



results in particular cases have been given. Theoretically it 

 should be the same that is to say, if a fall of 772 Ibs. 

 through a space of one foot will raise the temperature of 1 Ib. 

 of water through one degree of Fahrenheit, then the fall in 

 the temperature of 1 Ib. of water through one degree of Fah- 

 renheit should be able to raise 772 Ibs. through a space of 

 one foot. The calculations of M. Seguin are not far from 

 this, but since the elaborate experiments of M. Regnault he 

 has expressed some doubt of the correctness of his former 

 estimate, as by these experiments it appears that, within cer- 

 tain limits, for elevating the temperature of compressed va- 

 pour by one degree, no more than about three-tenths of a de- 

 gree of total heat is required ; consequently, the equivalent 

 multiplied in this ratio would be 1,666 grammes, instead of 

 500. Other investigators have given numbers more or less 

 discordant ; so that, without giving any opinion on their dif- 

 ferent results, this question may be considered at present far 

 from settled. M. Regnault himself does not give the law by 

 which the ratio of heat varies with reference to the pressure, 

 and is still believed to be engaged in researches on the sub- 

 ject one involving questions of which experiments on the 

 mechanical effects of elastic fluids seem to offer the most pro- 

 mising means of solution. 



I have endeavoured to give a proof (by showing the 

 anomaly to which the contrary conclusion would lead) that, 

 whatever amount of mechanical power is produced by one 

 mode of application of heat, the same should, in theory, be 

 equally produced by any other mode. But in practice the 

 difference is immense ; and therefore it becomes a question 

 of great interest practically to ascertain what is the most 

 convenient medium on which to apply the heat employed, and 

 the best machinery for economising it. One great problem 

 to be solved is the saving of the heat which the steam in or- 

 dinary engines, after having done its work, carries into the 

 condenser, or, in the high-pressure engine, into the air. It 



