W. J. M Raukine, Esq., on the Elasticity of Vapours. 33 



The formula may therefore be considered as accurately re- 

 presenting the results of all M. Regnaulfs experiments 

 throughout a range of temperatures from 30" of the centigrade 

 scale below the freezing point to 230° above it, and of pres- 

 sures from 2 2^00 of an atmosphere up to 28 atmospheres. 



It will be observed that equation (1.), bears some resem- 

 blance to the formula proposed by Professor Roche in 1828, 

 viz. : 



Loff P=:A--5_ 



^ T+C 



where T represents the temperature measured from the ordi- 

 nary zero point, and A, B, and C, constants, which have to 

 be determined from three experimental data. It has been 

 shewn, however, by M. Regnault, as well as by others, that 

 though this formula agrees very nearly with observation 

 thx'oughout a limited range of temperature, it errs widely 

 when the range is extensive. I have been unable to find 

 Professor Roche's memoir, and I do not know the reasoning 

 from which he has deduced his formula. 



The use in computation of the equations I have given, 

 whether to calculate the pressure from the temperature, or 

 the temperature from the pressure, is rapid and easy. In 

 Table II. they are recapitulated, and the values of the con- 

 stants for different measures of pressure and temperature are 

 stated. 



In calculating the values of «, the specific gravity of mer- 

 cury has been taken as 13596. 



Temperatures measured by mercurial thermometers are in 

 all cases to be reduced to the corresponding temperatures 

 on the air-thermometer, which may be done by means of the 

 table given by M. Regnault in his memoir on that subject. 



Table II. Vapour of Water. 



Formula for calculating the Maximum Elasticity of Steam 

 (P_), from the Temperature on the Air-Thermometer, 

 measured from the Absolute Zero (f) : 



Log l> = a % 



VOL. XLVII. XO. Xrill. — JULY 1849. c 



