410 MR. C. T. E. WILSON ON THE CONDENSATION NUCLEI PRODUCED IN 
to the rays. No trace of the nuclei can, however, be detected 30 seconds after 
cutting oft' the rays. The rapid diminution of the number of the nuclei is readily 
explained, if we regard them as consisting of positively and negatively charged ions 
which tend to recombine and neutralize one another. 
Experiments were also made with carbonic acid. 
CO 2 EXPOSED to X-rays. 
B = barometer reading = 768 millims. ; t = temperature = 21 ° C. ; tt = vapour 
pressure at i° C. = 18 millims. ; m = pressure required to sink plunger = 0. 
Gauge reading (in millims.) = ]). 
, B - - + 
’•J"' - B - . - p- 
Result of expansion. 
189 
1-337 
No drops 
190 
1-339 
190 
1-339 
Very few drops 
192 
1-344 
Slight shower 
235 
1-45 
Dense fog shoudng colours 
Least value of with which condensation was observed = 1'339. 
Even with an expansion the same as in the last observation given in the table, only 
a slight shower was obtained in the absence of the rays. 
The expansion, found in the previous experiments (‘ Phil. Trans.,’ loc. cit.) to be 
necessary to cause rain-like condensation to take place in the absence of X-rays, was 
Vojv^ = 1'36. Dense condensation began at the limit Vojvi = L53. In the experi¬ 
ments now described, condensation was again found to begin in the absence of the 
rays when rq/Pi = D36. 
The experiments with COo were made with a thin glass cloud chamber, such as is 
shovm in fig, 1. 
4. Nuclei peoduced by Uranium Rays. 
In the experiments on the action of the uranium rays on condensation, described in 
a previous paper (‘ Camb. Phil. Soc. Proc.,’ vol. 9, p. 333), the air was contained in a 
glass vessel v\^hich the rays had to penetrate; by far the larger part of the radiation 
being thus absorbed before it reached the air. Experiments were, therefore, performed 
in which the uranium compound was inside the vessel and thus actually in contact 
with the air, so that the maximum intensity of the radiation urns obtained. 
For this purpose the apparatus used was that shovui in fig. 1, the cloud chamber 
being a thin glass bulb. Inside it was fixed, by means of a copper wire vmund round 
the top of the narrow prolongation of B, a small shallow glass cup containing some 
uranium oxide. 
