[ 243 J 
XXXV.—ON THE MAXIMUM TENSION OF VAPOURS 
NEAR CURVED LIQUID SURFACES, sy GEO. FRAS. 
FITZGERALD, m.a., F.t.¢.D. 
° 
[Read June 16th, 1879. ] 
In the year 1870 Sir Wm. Thomson pointed out in the Pro- 
ceedings of the Royal Society of Edinburgh, that the maximum 
tension of vapour near a curved liquid surface must be different 
from that near a flat one. 
I have not come across any reference to an explanation of this 
fact, and propose the present one, though it is so obvious that I 
fear it must have been proposed before. 
It is generally received that the tension of vapour in contact 
with its liquid attains equilibrium when the number of molecules 
emitted by the liquid per unit of time per unit of surface is equal 
to the number of those admitted similarly. Hence, any cause 
which tends to increase the former and decrease the latter must 
increase the tension. 
In estimating the numbers of molecules emitted from a 
spherical drop I shall assume that they are emitted from all 
points of a stratum, of a very small depth, and that the number - 
of those emitted in a particular direction from a point is a 
function of the distance they have to travel inside the stratum. 
Let a be the radius of the drop, and 6 the length of the radius 
to the emitting point, which is less than @ by the very small 
quantity t, which is the depth of the emitting point below the 
surface of the drop. Let v be the distance from the end of b to 
any point on the surface, and let f(v) represent the proportion 
emitted, which traverse a length v in the stratum, then the 
number emitted from the depth ¢, in the direction between v and 
v + dv, may be written 
; ora - 1 
ons, uf (v)dv . dt 
Scien. Proc., R.D.S. VOL. 11, PT-1Vv. S 
