166 



Mr. C. V. Burton on the Value 





Supplementary 



Observations. 





Date. 



Time. 



Temp. 



Elongation. 



April 25 



9.30 p.m. 

 10.0 

 10.45 



9.20 

 10-20 



9.20 

 11.0 

 11.20 

 10.0 

 11.0 

 11.0 



7.45 



9.20 



9.15 



8.50 a.m. 



49-0 

 48-5 

 50-8 

 63-7 

 54-5 

 500 

 48-6 

 458 

 48-6 

 56-8 

 51-8 

 510 

 52-5 

 590 

 54-7 



24-5 



230 



22-5 



23-0 



25-0 



24-5 



25-5 



23-5 



400 



86-0 



118-0 



124-0 



124-5 



1240 



143-5 



„ 25 



„ 26 



„ 27 



„ 28 



„ 29 



„ 29 



„ 30 



May 4 



4 



5 



6 



6 



8 



„ 10 





XIX. On the Value of "y" for a Perfect Gas. 

 By Chables V. Burton, J5.Sc. (Lond.).* 



fj^HE ratio, 7, between the two elasticities or the two spe- 

 X cine heats has been measured, in the case of gases, by 

 various experimental methods. Some of these methods are 

 based on the assumption that the gas in question may be con- 

 sidered approximately perfect. 



The object of the following investigation is to show that 7 

 has the same value (§) for all perfect gases, and can be cal- 

 culated for this hypothetical class of bodies from purely 

 theoretical considerations. 



Let us take a certain portion of perfect gas whose volume 

 is v, pressure p, and molecular kinetic energy W. The iso- 

 thermal elasticity of the gas under these conditions, 



'Et—p- 



Now, in order to find the isentropic elasticity, let the gas be 

 compressed adiabatically until its volume is diminished by dv, 

 the volume after compression hemgv.^v — dv : and the pres- 

 sure being at the same time increased to p x =p + dp. 



* Communicated by the Author. 



