476 M. Regnault's Researches upon the 



escaping from the engine, that is to say, in short, equal to the 

 loss of heat hv the air in traversing the engine. But as, ac- 

 cording to Ericson's system, the heat which the air possesses 

 at the time of its escape is deposited in the substances from 

 which the fresh air in entering abstracts it in order to convey it 

 back again into the engine, it is evident that, theoretically 

 speaking, in these latter engines all the heat is rendered available 

 for the mechanical work ; while in the best constructed engines 

 worked by water-vapour the heat rendered available for mecha- 

 nical work does not amount to ^\yth of that generated. It must, 

 however, be remembered that I do not here take into considera- 

 tion the exterior losses, such as mechanical or industrial obstacles, 

 which may present themselves in practice. 



MM. Joule, Thomson, and Rankine in England, MM. Mayer 

 and Clausius in Germany, setting out from different points of 

 view, have developed mathematically the mechanical theory of 

 heat, and they have endeavoured to deduce from it the laws of 

 all phaenomena relating to all elastic fluids. I have, for my o\(M1 

 part, long put forward in my lectures analogous views, to which 

 I have been led by my experimental researches upon elastic 

 fluids. In the course of those researches, I have encountered 

 indeed at every step anomalies which appeared to me inexplicable 

 in accordance with the theories formerly recognised. For the 

 sake of illustration I will quote some of the most simple in- 

 stances : — 



First Example. — 1. A mass of gas under a pressure of 10 

 atmospheres is contained in a space which is suddenly doubled ; 

 the pressure falls to 5 atmospheres. 



2. Two reservoirs of equal capacity are placed in a calorimeter ; 

 the one is filled with gas under a pressure of 10 atmospheres, 

 the second is perfectly empty. When a communication is sud- 

 denly made between the two reservoirs, the gas expands to 

 double its volume, and the pressure is reduced to 5 atmospheres. 

 In these two experiments, then, the initial and final conditions 

 of the gas are the same ; but this identity of conditions is ac- 

 companied by calorific results, which are very different; for 

 while in the former experiment there is a considerable reduction 

 of temperature, in the second the calorimeter does not indicate 

 the slightest alteration of temperature. 



Second Example. — 1. A mass of gas M traverses under the 

 ordinary atmospheric pressure a winding tube in which it is 

 heated to 212° F., and then a calorimeter whose initial tempera- 

 ture is 32° F. The temperature of the calorimeter is raised / 

 degrees. 



2. An equal mass of the gas traverses, under a pressure of 

 10 atmospheres, the winding tube, in which it is heated to 



