"Specific Heat of Saturated Ether Vapour." 291 



and at pressures from 1 to 25 metres of mercury. His 

 numbers, which are reproduced in the last column but one of 

 the above table, combined with those in the second column 

 (which are Ramsay and Young's), will give the numbers in 

 the last, which, compared with the values above obtained, 

 may convince lis that we are not far from the truth. 

 Hence I obtained the following values for 



c -H. 



t. 



fd v \ 



fdv\ _ 





cp—TS.. 



+120° 



cm. 

 15395 



c.cm. 

 0-00537 



c.cm. 

 0-00570 



grm.-cal. 

 0-01096 



100 



11-048 



419 



432 



0-00564 



80 



7-700 



334 



341 



0-00294 



60 



5062 



277 



281 



0-00150 



40 



3-116 



272 



274 



000085 



20 



1-759 



220 



221 



0-00036 







0-884 



214 



214 



0-00016 



These will show that the difference under consideration 

 rapidly decreases as the temperature falls, and that errors 

 introduced into the value of h through neglecting that dif- 

 ference will be about 1 per cent, (on the assumption that h 

 is of the order of +0'1 calorie) so long as we confine our- 

 selves to temperatures below 4-40° or even +60°, but will 

 amount to as much as 10 per cent, when we go so far as 

 4-120°. 



The temperature +40° is nearly the upper limit within 

 which the empirical formula for the specific heat of liquid 

 ether was obtained by Regnault : 



c p - 0*52901 +£-0005916.*. 



This is not, of course, to be extended without sufficient 

 reasons to higher temperatures, and, therefore, we must not 

 receive without reservation Clausius's calculation of v and 

 subsequent evaluation of h at higher temperatures from 

 Kegnault's data. 



In the following discussion, then, we shall not extend our 

 considerations far beyond the temperature 4-40°. 



Now, when we make use of the above formula for c p , we 

 make tacitly another assumption, namely, that the influence 



Y2 



