114 
DRS. W. RAMSAY AND S. YOUNG ON SOME OF 
Rankine (‘ Edinb. Trans./ vol. 23, Part I., 1862, p. 147) discusses the want of 
concordance between the volumes of saturated steam observed by Fairbairn and 
Tate, and those calculated from Regnault’s observations on the beats of vaporization ; 
and suggests a difference in molecular condition between steam at rest, as in 
Fairbairn and Tate’s experiments, and in motion, as in Pegnault’s. It can 
scarcely be doubted that the true reason of the discrepancy is to be found in the 
adhesion of steam to glass. It is obvious that in Regnault’s experiments this source 
of error would be absent, inasmuch as the weight of water was simply that which 
entered the calorimeter. 
Three sets of isothermal curves were drawn in which the experimental numbers 
were closely followed, the only adjustment being that of rendering the curves as 
smooth as possible, and of making use of the mutual relations between the curves, so 
as to smooth out the irregularities of each individual one. These curves were pro¬ 
longed to the points calculated from Regnault’s observations by the formula 
. _ LJ ■ 
5l T dp/dt S ’ 2 ’ 
where s L and s 2 are respectively the volumes of saturated vapour and liquid, L the 
heat of vaporization, J the mechanical equivalent of heat, T absolute temperature, 
and dpjdt the differential of pressure in degrees with respect to temperature. 
By help of this formula the following table was calculated :— 
