202 M. Achille Cazin on Internal Work in Gases. 



by the side sin A is greater than that withdrawn by the side sin B ; 

 the exchanges of motion and heat will be accomplished in a space 

 which receives heat at the same time, and the temperature will 

 end by being higher than the initial temperature. From this 

 moment the gaseous mass will slowly return to the exterior tem- 

 perature, losing exactly the heat which it had gained. It is 

 sufficient for this effect to be possible that the heat should spread 

 more rapidly in the gas than in the sides. Since such is the 

 effect observed, we are able to say from experiment that the heat 

 given up by the sides in A exceeds the heat withdrawn in B. 



Let us now examine what results from a modification of the 

 reservoir B. 



The reservoir A being the same, the heat given up to the gas 

 which is there does not change; but things are different in re- 

 servoir B. The gas which at first filled it under the pressure jo 2 

 has been compressed, supporting an exterior pressure nearly 

 equal to its elastic force, and it has passed from the pressure jo 2 

 to the final pressure p 1 . By increasing the capacity of reservoir 

 B we have increased p q , so that the rise of temperature of this 

 part of the gas has diminished. But we have increased the mass 

 and the surface of this part, and by substituting glass for zinc 

 we have increased the absorbing-power of the sides. Hence 

 it may happen that the heat withdrawn from this part is in- 

 creased a little. As to the gas which passes from A to B, the 

 changes which it undergoes during the passage are very complex. 

 We know, from an experiment made by Gay-Lussac, that the 

 temperature is different every moment at the various points of a 

 rarefied reservoir into which a jet of gas rushes : the tempera- 

 ture falls in the layers near the orifice ; in those more distant it 

 rises : moreover the magnitude of these effects varies progres- 

 sively with the time. Hence there are in our experiment con- 

 trary thermal actions between the sides and the jet of gas. 

 Certain parts of the jet take heat from the sides ; others give up 

 heat to them. But this complexity only occurs during the 

 efflux, which is of very short duration ; in my experiments it was 

 less than Ol second; and when the efflux stops, the mean tem- 

 perature of the part considered differs less from that of the sides 

 than does that of the other two parts. Hence the direction of 

 the action of the sides depends especially on the condition of 

 those two parts. 



If the heat withdrawn from the gas is less in the zinc reser- 

 voir than in the glass one, the excess of heat gained in reservoir 

 A over the heat withdrawn is greater, and consequently the 

 curve of the A's rises more with the first than with the second ; 

 this is the effect observed. Thus the difference of the maxi- 

 mum of h is explained by the cooling action of the glass, which 



