34 A. W. Witkowski on the 



0=-14O°, Cj =0*169 + 0-0135 0-1), 

 0=-135°, c=0-169 +0-00722 (p- I), 

 (9= -130°, ^=0-169 + 0-00432 (p-1), 

 0=-lO3\5,r; = 0*169 + 0*00056 0-1), 

 0=- 78°-5, ^=0-169 +0-00038 0-1), 

 0=- 35°, c c = 0-169+ 0-00024 (p-l) 9 

 0= 0°, c=0*169 +0-00008 0-1). 



As regards tlie fact of the specific heat at constant volume 

 increasing with increasing pressure, these results are in 

 perfect accord with the direct determinations of Proi. Joly. 

 A numerical comparison cannot be made properly, because 

 these experiments have been performed at higher temperatures 

 ( + 50° in the mean). Yet the following result of Prof. Joly 

 may be quoted (I. c. page 99). The specific heat at constant 

 volume of compressed air, of absolute density =0 0205 (which 

 corresponds to a pressure of about 19 '51 atmospheres), has 

 been found =0*1721 ; from the same experiments it is con- 

 cluded, that the value of c v under atmospheric pressure would 

 be 0*17154. From these numbers there results an increase 

 of c v , per atmosphere 



= (0*1721-0-17154) : 18*51 = 0*00003. 



Considering the difference of temperatures, this agrees well 

 with my own results. 



Prof. Joly has also investigated the influence of the tempera- 

 ture on the specific heat c v of compressed gases. For carbonic 

 acid of absolute density 0*124 he finds ^ = 0*1971 at +50°, 

 and ^ = 0*1894 at +90° ; this means an increase of specific 

 heat at low temperatures. He remarks also, that under small 

 pressures the influence of the temperature is quite insensible. 

 All these conclusions are in perfect agreement with what has 

 been said above with regard to the specific heat of air. 



§ 16. By means of the results arrived at in § 14 we may 



now calculate the ratio k = -£ of the two specific heats; the 



c v 



values of k are given in the tables of § 14 in the last column. 

 The general features of the variations of k will be best under- 

 stood if we consider k as a function of the temperature, at 

 constant volume, or at constant density. The corresponding 

 curves are shown in fig. 6. 



With regard to the variability of k our knowledge is ex- 

 ceedingly scanty. The only fact known till now in this respect 



