414 HENEY A. ROWLAND 



Also, 



J= ~ ~^(!*L\ ~^L' 

 \ dp ),,, V 



Application to gases; Rankine's formula is, 



(4L) SB A/1 + *,*L *.}, 



\ d/j. h ii \ ;j. v J 



dp- 1 - -, - . 1 + 



If a.v is the coefficient of expansion between and 100, then 



AI, = (1 + -00635m), 

 whence 



where a' p and a, are the true coefficients of expansion at the given 

 temperature; 



+ 5m *.*. 



According to Thomson and Joule's experiments m = 0-33 C. for air 

 and about 2-0 for C0 2 . Hence //= 272 -99. 



The equations should be applied to the observations directly at the 

 given temperature, but it will generally be sufficient to use them after 

 reduction to C. Using K = -2375 according to Regnault for air, we 

 have for the latitude of Baltimore, 



From Rontgen's value r = 1-4053 = 430-3. 33 



J 



" Amagat's " 1-397 = 436-6. 



" velocity of sound 331-78m. per sec. = 429'6. 



*/ 



33 R6ntgen gives the value 428-1 for the latitude of Paris as calculated by a formula 

 of Shroder v. d. Kolk, and 427-3 from the formula for a perfect gas, and these both 

 agree more nearly with my result than that calculated from my own formula. 



