84 
MR. r. V. SEVAN ON THE COMBINATION OF HYDROGEN 
Time 
from beginning of 
insolation. 
Expansion. 
Experiment HI. 
Experiment I. 
Experiment II. 
1 
3 
3 
1 
5 
2 
18 
26 
22 
3 
34 
51 
41 i 
4 
47 
73 
59 
5 
60 
90 
79 i 
6 
73 
106 
91 j 
7 
84 
119 
105 
8 
92 
128 
115 1 
9 
99 
131 
123 i 
10 
104 
132 
130 1 
11 
107 
— 
132 I 
12 
108 
■ ■ 
1 
These experiments also show that the rate of expansion increases with the time of 
illumination at first and then dimioishes until the expansion is complete. After this, 
contraction at once sets in. Now it might he tliought that this observed increase in 
the rate of expansion might simply be due to the inertia of the water index in the 
caj)illary tube—the viscosity of the water would tend to diminish the acceleration ot 
the expansion. To perform a series of experiments that would eliminate this elfect of 
inertia a series of illuminations, each lasting for one second, was made. Each 
illumination followed (juickly on the preceding one, only sufficient time being allowed 
between the illuminations for the index to come nearly to rest. Tlie actual interval 
between the observations below was from 10 to 15 seconds. In the following tables 
are v-iven in the first column the numbers of the illumination of one second from the 
o 
first, which was made with fresh gas that had always been in the dark. In the 
second column is the expansion observed for each illumination. The intensity of the 
light was different in the different experiments. 
