306 
MR. C. T. R. WILSON ON CONDENSATION OF WATER VAPOUR 
Radius, in centims,, of drops just large enough to grow in vapour supersaturated to 
the extent required to make rain-like condensation begin in the presence of Air. 
f 0 . 
e. 
T. 
S. 
r. 
-10 
263 
77 
4'35 
8-7x10-8 
- 6 
267 
76 
4-2 
8-6 X 10-8 
+ 2 
275 
75 
4-0 
8-6 X 10-8 
O' thus appears to be constant over the range of temperature — 10 ° C. to + 2 ° C. 
The value obtained for o' is not changed by as much as 3 per cent, when the air 
is replaced by nitrogen, oxygen, or CO^, or by hydrogen under the action of 
the X-rays. 
Radius, in centims., of drops just large enough to grow when supersaturation is 
sufficient to make the dense condensation begin in Air, Oxygen, Nitrogen, or 
Hydrogen. 
f C. 
e. 
T. 
S. 
r. 
-16 
257 
78 
7-9 
6-4 X 10-8 
If we consider the difference in the value found for S in CO^ to be real, and 
not due merely to the error in the calculation of the cooling, due to deviation 
of CO 3 from the condition of a perfect gas, we find that r in CO 3 is about 3 per cent, 
greater than in these other gases. 
Radius, in centims., of drops just large enough to grow when the supersaturation 
is such that the sensitive tint is produced in the presence of Air or Oxygen. 
f C. 
0 . 
T. 
S. 
7', 
-19 
254 
79 
9-9 
5-9 X 10-8 
The difference when nitrogen is substituted for Air or Oxygen is exceedingly 
small. 
It cannot be assumed that the surface tension retains its ordinary value in drops 
of such small radii, which are not great compared wfith molecular dimensions. AYe 
know, in fact, from the behaviour of thin films, that it does not. These numbers 
therefore can only be considered as giving a very rough approximation to the 
