M. Achille Cazin on Internal Work in Gases. 85 



transforming it into a kind of gas-thermometer*. In order to 

 do this he divided a cylinder into two compartments by means 

 of a membrane, and adapted an oil-manometer to it. The gas 

 being at first under the same pressure in the two compartments 

 and in the manometer, the latter was closed, and by means 

 of a pump the gas was made to pass from one of the compart- 

 ments into the other. The membrane was then burst by al- 

 lowing a weight to fall upon it, and the manometer was imme- 

 diately opened. No displacement in the levels of the manome- 

 tric liquid was observed; so that the apparatus revealed neither a 

 creation nor a disappearance of heat. We shall see in the course 

 of this memoir how complicated is the phenomenon ; I will only 

 at present remark that Messrs. Joule and Hirn only sought to 

 observe the final thermic effect. 



It is also in order to investigate the final effect that the for- 

 mulae of the thermodynamic theory have been applied to this 

 phenomenon. M. Bauschinger has published a long treatise on 

 this subjectf. But he has assumed Mariotte and Gay-Lussac's 

 laws, and consequently all the formulae which he has given are 

 not verified by experiment. 



Messrs. Joule and Thomson calculated the final thermal effect 

 in question without assuming Mariotte and Gay-Lussac's laws J. 

 They found that there must be a fall of temperature of 2°'8 for 

 air under a pressure of twenty-one atmospheres when it was 

 allowed to flow into an empty vessel of the same capacity as 

 the first. As to the thermometric effect produced in the water 

 which surrounded the apparatus, it was required to be only 0°*003, 

 a quantity almost inappreciable. 



There is another mode of observing the thermal effects which 

 accompany the expansion of gas when the external work is none, 

 or at least very little, and when the external calorific action may 

 be neglected. It has been employed by Messrs. Joule and 

 Thomson for various gases §, and by M. Hirn for aqueous va- 

 pour || . The compressed gas flowed into the atmosphere under 

 a constant pressure through one or more small orifices. At a 

 certain distance from the orifice it impinged upon a thermome- 

 ter-bulb properly sheltered, and the current was kept up suffi- 

 ciently long for the thermometer to become stationary. A fall 

 of temperature was always observed. Messrs. Joule and Thom- 



* G. A. Hirn, Exposition analytique et experiment ale de la Theorie me- 

 canique de la Chaleur, p. 52 (18fi5). 



t In Schlomilch's Zeitschrift fur Mathematik und Physik, vol. viii. 



X Transactions of the Royal Society of London, vol. cxiiv. p. 344 (1854). 



§ Transactions of the Royal Society of London, vols, cxliii. & cxliv. 

 (1854). 



|| G. A. Hirn, Exposition analytique et experimentale de la Theorie m6- 

 canique de la Chaleur, p. 177 (1865). 



