44 
MR. J. J. WATERSTON ON THE PHYSICS OF MEDIA COMPOSED OF 
— ( „) = ?/o — G tan H, or tan H 
= V, 
461 + t 0 x 461 + t 0 — G 
-; and by 2nd 
experiment tan H = 
461 + q V 461 + t 1 —■ G 
From these we eliminate* 
G = 
-- 6 / 4:6 1 “h tr\ 6 \ /-—- 
v/461 + t 461 + q X 7 0 ~ V 7461 + ^ + 
vim x - 1 -1 
461 + q 
From the two observations corresponding to the points S and F, I have computed 
the value of G = 19'4923 and tan FI = (P09230S, which define the equation for the 
steam line that best answers to the experiments of Southern and the French 
Academy combined. This equation is tan 6 FI (y/461 + t — G) 6 (461 + t) — e, or by 
putting cot H as the common denominator we have the following formula for the 
tension of steam at all temperatures :— 
+ t - 19-4923 
10-883 
(461 + t) = e (in inches of mercury). 
It is singular that the points of projection belonging to each of the many sets of 
experiments on steam range themselves in a line, but these lines do not coincide, 
except in the case of Southern and the French Academy. Each set is thus con¬ 
sistent with the general law, and on this account their want of accordance with each 
other is difficult to explain. It might be caused by an error of the standard scales, 
but this is hardly possible; or impurity of the water, which is not very likely where 
every precaution has been so carefully attended to. Dr. FTre’s line of observations 
is more inclined to the axis than SF, the cot II in the formula being 10'3 and G = 19*8. 
The line of the American Institute’s experiments has yet a greater elevation, the 
cot H being about 9'8. 
The other lines of vapour on the chart explain themselves. It will be remarked 
that the deflections from the straight are all of a zig-zag character, there is no general 
bending to one side or another, and this seems to show that there is some physical 
law upon which the equilibrium of vapours with their liquids is arranged that is 
represented by the above function of the temperature. As it seems to apply to all 
vapours, it is probably not beyond the grasp of physical research, if the vis viva 
theory is admitted, for it evidently does nut depend on the chemical qualities of 
the body any more than does the law of volumes in gases. 
It must be confessed that as yet we have but few materials wherewith to found a 
process of investigation. The fundamental point is the specific heat of steam. 
* [P determine.—R.] 
f If Dalton and Gay-Lussac’s constant of expansion is preferred, 448 is to be substituted in tbe place 
of 461. 
