M. V. Regnault on the Expansion of Gases. 133 



fectly comparable, the velocity of the gas in emerging from the 

 calorimeter should be exactly the same. It would be particularly 

 interesting to arrange the apparatus and conduct the experiments 

 so that the velocities of transport of the expanded gas were 

 the same, on emerging from the calorimeter, as those which they 

 possess when they arrive with their initial pressure in the first 

 tube of the calorimeter. For this purpose the sections should 

 be inversely as the densities of the gases. I have not, however, 

 attempted to realize this condition in the experiments I have 

 just described. 



It would also be of great interest to know the value of y 1 when 

 the gas emerges from the calorimeter with an infinitely small 

 velocity ; this would be the limit ofy. It is clear that this can- 

 not be attained merely by a calorimetrical method ; for the con- 

 ditions cannot be realized in which the gas finally assumes the 

 state of rest and remains constantly at the same temperature as 

 the calorimeter. It could only be obtained by determining very 

 accurately the temperature of the gas on its emerging from the 

 calorimeter, and the velocity of the current at the place where 

 the bulb of the thermometer which gives this temperature is 

 placed. In my memoir many experiments are given in which I 

 have endeavoured to determine the temperature of the gas on its 

 emergence ; but this determination always presents uncertainties. 



III. Calorific effects produced by air which expands in traversing 

 more or less long capillary tubes. (Experiments of 1854.) 



In my first mode of working, the air suddenly expands on 

 emerging from a single capillary orifice perforated in a thin plate. 

 In the second the expansion was made successively on passing 

 through twelve orifices in thin plates placed at equal distances 

 from each other. In the third method, which I am about to 

 describe, I wished the expansion to take place in an absolutely 

 continuous manner, the air traversing a very long capillary tube. 

 The air reached the entrance of this tube under a pressure very 

 little different from that which it had in the large reservoir, and 

 on escaping from this tube it met a pressure very little different 

 from that of the atmosphere. I was especially desirous of ascer- 

 taining thus whether the friction of the air on a great length of 

 tube-wall modified to any perceptible extent the calorific effects 

 produced by the simple expansion of the gas. 



The large reservoir in which the air is compressed is hermeti- 

 cally connected with the end of a long copper worm placed in 

 a bath filled with water at the surrounding temperature. The 

 other end of this worm is hermetically cemented to the com- 

 mencement of the worm placed in the calorimeter. 



The worm of the calorimeter consists of two copper tubes 



