8 



Prof. Buff on the Relation between the 



account of the variable value of a, not being directly fitted for 

 this purpose. Without employing formula (9), however, the 

 temperature can now be derived from the tension by means of 

 the values of a given in the Table. 



Suppose we find n in equation (10) to be 1*5 atmosphere, the 

 value a = 13*0797. The next higher number in the Table, 

 13*1182, corresponds to a temperature of 110°. The propor- 

 tional number pertaining to it, in other words, the decrease of a 

 for 1° C, is 218, and the difference is 



13*1182-13*0797=00385. 

 The ratio therefore is 



218: 385 = 1° :1°*76. 



The desired temperature is 111°*76, or 1°'76 higher than 110°. 

 The numbers representing the magnitudes of the tensions of 

 aqueous vapour which Dulong and Arago* obtained from their 

 observations in the year 1828 are in terms of atmospheric pres- 

 sure. In the Table given by Regnault the tension is expressed 

 in millims. of mercury. We are consequently unable to judge 

 of the degree of agreement which exists between the old and the 

 new measures. The following Table, wherein some of the num- 

 bers calculated from Regnault's observations are placed by the 

 side of the corresponding ones of Dulong and Arago, may there- 

 fore be acceptable : — 



Pressures in 











atmospheres 

 of 070 me- 







T° C. 





a. 









tre of 











mercury. 





B. 



D. and A. 



E. 



1 



13-3442 



100- 



100 



100 



2 



12-8901 



120-63 



121-4 



120-69 



3 



12-6202 



133-93 



1351 



13418 



4 



12-4267 



14402 



145-4 



144-40 



5 



12-2755 



152-25 



1531 



152-76 



6 



121513 



159-26 



160-2 



159-88 



7 



120458 



165-39 



166-5 



166-10 



8 



11-9540 



17087 



1721 



171-66 



9 



11-8728 



175-83 



1771 



176-68 



10 



117999 



180-37 



181-6 



181-27 



15 



11-5173 



198-87 



200-5 



199-90 



20 



11-3149 



213-06 



214-7 



21408 



25 



111568 



224-75 



226-3 



225-65 



30 



110269 



234-77 



236-2 



235-50 



Column E. in the above Table is extracted from Dove's Reper- 

 torium der Physikf. The numbers contained therein were com- 

 puted by means of an empirical formula which Egen J developed, 



* Poggendorff's Annalen, vol. xviii. p. 437. 



t Vol. i. p. 47. 



% Poggendorff's Annalen, vol. xxvii. p. 9. 



