408 MR. C. T. R. WILSOX ON THE CONDENSATION NUCLEI PRODUCED I^n 
Carbonic acid was prepared by heating potassium bicarbonate. In each case the tube 
in which the gas was produced was fused to the rest of the apparatus with the blow¬ 
pipe. 
§ 3. Nuclei produced by X-rays. 
In the experiments with X-rays described in the ‘ Phil. Trans./ loc. cit., the gas 
was only exposed to such radiation as was able to penetrate glass. It was of interest 
to know whether under the action of strong radiation condensation would take place 
with a less degree of supersaturation, or rvhether merely the number of nuclei would 
be increased. In a postscript to that paper the results of further experiments were 
given, showing that the latter alternative was the true one. Further experiments 
have confirmed this. 
For the experiments with X-rays the expansion apparatus used differed from that 
represented in fig. 1, in being without the part A, the tube B being cut off square at 
the top instead of being prolonged into a narrower tube. With the help of an india- 
rubber washer, its upper end, which was ground smooth, was closed by a thin sheet 
of aluminium. This was held down by a brass diaphragm, which was screwed tight 
by three bolts, attached to a similar brass plate pressing against the lower surface of 
the indiarubber stopper which closes the lower end of B. 
A “ focus ” tube giving out strong X-radiation was fixed a few centimetres above 
the aluminium plate closing the top of the tube B. In some of the experiments the 
expansion apparatus was wrapped in tinfoil (provided with the necessary apertures 
for observing the result of the expansions) ; this was found to be without effect on 
the appearance of the fogs. 
The results of expansions in the immediate neighbouilrood of the jioint where con¬ 
densation first begins are given below. 
I. Air exposed to X-rays. 
B = barometer reading = 767 millims. ; t = temperature = 18° C. ; tt = maximum 
vapour pressuiB at C. = 15 millims. ; m = pressure required to sink 
plunger = 0 millim. 
Gauge reading (in millims.) = 
, B - TT + m 
Result of expansion. 
B - ir - p 
146 
1-241 
No drops 
149 
T247 
Very few ckops 
156 
T259 
Fog 
Least value of Vo/v^, with which condensation was observed = 1'247. 
When the expansion was made without exposure of the air to X-rays, only a very 
few scattered drops were seen even with as great as 1'279. 
Similar results were obtained with oxygen. 
