as applied to Ga^es and Vapours. 523 



For the Centigrade scale, C = 274°'6, being the reciprocal of 

 0-00364166. 



For Fahrenheit's scale, if adjusted so that 180° are equal to 

 100° Centigrade,— 



C for temperatures measured from the freezing-point of water 

 = 494°-28. 



C for temperatures measured from the ordinary zero 

 = 494°-28 - 32° = 462°-28. 



The point C degrees below the ordinary zero of thermometric 

 scales may be called the absolute zero of temperature ; for tempe- 

 ratures measured from that point are proportional to the elasti- 

 cities of a theoretically perfect gas of constant density. 



Temperatures so measured may be called absolute temperatures. 

 Throughout this paper I shall represent them by the Greek letter 

 T, so that 



T=T + C (15) 



It is to be observed, that the absolute zero of temperature is 

 not the absolute zero of heat. 



(18.) If we now substitute for P in equation (13) its value 

 according to equation (I2fl), we obtain the following result : — 



Let n represent, as before, the theoretical number of atoms in 

 unity of volume, under unity of pressure, at the temperature of 

 melting ice, of the gas in question, supposing the disturbing 

 forces represented by — F(D, ^) and/(D) to be inappreciable; 

 then nM is the weight of unity of volume under those circum- 

 stances, and it is evident that 



I> TIT 



p-=/iM. 

 Consequently 



r=T+C=C.;.(^+6), .... (16) 



being the complete expression for that function of heat called 

 temperature. 



It follows that the function 6, which enters into the expres- 

 sions for the elasticity of gases, is given in terms of temperature 

 by the equation 



^=^+1=0^ (i«^) 



If, according to the expression 4, for the quantity of heat in 

 one atom, we substitute -^ for v^ in equation (16), we obtain 



