com 



180 Mr. T. R. Edmonds on the Elastic Force of 



the place of the absolute zero of temperature in respect of densi- 

 ties of air in the proportion of 33 to 1. If a further reduction 

 in the density of the air in a similar proportion could have been 

 effected, it is not improbable that a coefficient of expansion equal 



to 2^ nearly would have been obtained, which coefficient of 



expansion is the constant quantity (- for temperature 0° C.) 



involved in all M. Regnault's experimental results on the elastic 

 forces of steam of maximum density at different temperatures. 



When the value of the constant a has been determined for 

 any fixed temperature, the only constant remaining to be deter- 

 mined is « in the general formula for the ratios of elastic 

 forces at all temperatures. As has been said, this quantity a 

 is the hyperbolic logarithm representing the increment per 

 degree of the elastic force at the precise absolute temperature a° 

 of the point fixed as the origin of thermometrical temperature t°. 

 In the construction of my theoretical Table, I have found it 

 most convenient to adopt 100° C. as the origin of the thermo- 

 metrical scale, so that the value of a in this case is 376°, being 100° 

 added to 276° when the latter is the value of a for the tempera- 

 ture of melting ice. The whole range of temperature observed 

 by M. Regnault is comprised between 130° above the tempera- 

 ture of 100° C, and 130° below that temperature. Consequently 

 if f be reckoned from 100° C, all thermometrical temperatures 

 referred to may be expressed in terms of the absolute tempera- 

 ture (a + t) or [a—t), wherein a = 376, and t is any quantity not 

 exceeding 130° C. The lowest absolute temperature observed is 

 246°, and the highest 506°. 



When the value of a has been obtained for any absolute 



temperature («), the value of ct t for any temperature greater by 



— — 

 t° may be obtained from the equation oi t =ct f 1 + - j . The 



value which I have adopted for a at 376° absolute temperature 

 is *03580. When this number is inserted in lieu of ct in the 

 general formula, we get, first, when t is positive, 



, _ kua 'f_ /, , t\~ n \ £x*0358x376 J\ / t \~ \ 



^-Ti 1 ^ 1 "^) ) = 1-302585 \}-\} + m) J 



= 4.487960{l-(l + 4)- TC }. 

 Secondly, when t is negative, 



comlogP_,= ~4-48796o|*^l-^g)~ n -l^ 



