lOG MR. P. V. BEVAN ON THE COMBINATION OF HYDROGEN 
on the formation of nuclei. For this purpose an expansion corresponding to 
Pj/P 2 =:I -35 (about) was used, as this expansion was well under the expansion 
required to produce condensation in the uninsolated gas. The following two tables 
give the results of two series of experiments, one with dim, the other with bright 
light :— 
I. Dim Light. P]/Po = 1*35. 
Time of insolation. 
Observation. 
1 second 
10 seconds 
30 „ 
40 „ 
, 60 „ 
i 4 minutes 
’ 10 „ 
1 
Only one or two drops observed. 
Several drops. 
Fine rain. 
Rain cloud. 
Cloud indistinguishable from the last. 
11 11 11 
II. Bright Light, Pi/Pj = 1‘35. 
Time of iusolation. 
Observation. 
1 second 
Fine rain. 
2 seconds 
More rain. 
3 „ 
Cloud. 
5 „ 
Thick cloud. 
10 „ 
Cloud incbstinguishable from the last. 
1 minute 
Same cloud. 
Experiments \vere next made on the gas after the illumination was cut off. The 
mixture M^as illuminated for some minutes before each expansion, and then the 
mixture was darkened and an expansion corresponding to P^/Po = 1’36 made after 
the time in the first column. 
Time from darkening 
to expansion. 
Observation. 
10 seconds 
Thick cloud. 
1 minute 
11 11 
2 minutes 
Cloud less than in last experiment. 
5 ,, 
Rain cloud. 
10 „ 
Fine rain cloud. 
1 hour 
Fine rain. 
2 hours 
A few drops. 
With chlorine alone similar results were obtained. 
The fact that the cloud produced in the mixed gases is similar to that produced in 
