106 Mr. Ivory on the Difference of 



Now it is manifest that, the mass of air remaining the same, 



the quantity '^., has the same value in all circumstances ; it 



is equal to ~^, putting M for the bulk of the given mass of 



air reduced to zero of the thermometer, the pressure being 

 constant. The first of the foregoing formulas is therefore, 



1 v-V 



The variation of temperature for the same change of volume, is 

 1 V-V 



a M 



> 1 13 1 



Now, in Fahrenheit's scale, — = 480°, and --• = - x • — , 



a /3 o a 



therefore, j = f x 480 x — ^ = 180° x -^^- . 



In order to find the heat /, we must therefore convert the dif- 

 ference of volume V — V, into degrees at the rate of 180° for 

 M, which is the bulk of the given mass of air at the tempera- 

 ture zero ; just as the heat of temperature is found by con- 

 verting the same difference of volume into degrees at the rate 

 of 480° for the same bulk M. In the second formula, we have 

 (1 + «fi) ^=1)5 T) being the density of the mass of air when 

 it is reduced to the bulk M ; and thus we readily obtain 



which is manifestly equivalent to the other expression. I am 

 not aware that it is possible to warp these formulas from their 

 obvious and unequivocal meaning; and as my sole intention is 

 to explain what I have written, and to rescue it from the 

 fangs of Mr. Meikle's algebra, which perverts whatever it 

 touches, it seems unnecessary to add any thing further. But 

 in quitting this subject, to which I will not return, I cannot help 

 expressing my surprise at finding myself involved in such petty 

 disputation. 

 Jan. 13, 1829. James IvoRV. 



XVI. On the Method of deducing the Difference of Longitude 

 from the Azimuths and Latitudes of two Stations. By 

 James Ivory, Esq. M.A. F.R.S. ^c* 

 T SHALL now extend to all solids of revolution that are 

 -*• little different from a sphere, the same property which is 

 proved of the oblate elliptical spheroid of revolution in the last 

 Number of this Journal. 



* Coniiminicated by the Author. 



Takiiifif 



