422 
MR. W. CROOKES OK THE VISCOSITY 
sidered that this variation from Maxwell’s law was due to some inherent property of 
all gases. After working at the subject for more than a year, it was discovered that the 
discrepancy arose from a trace of water obstinately held by the hydrogen—an impurity 
which behaved as I explain farther on (699) in the case of air and water vapour. 
Since discovering this property, extra precautions (already described at the commence¬ 
ment of this paper (641)) have been taken to dry all gases before entering the apparatus. 
The results are given in the following table :— 
689. Table VI.—Log. dec. of hydrogen gas at pressures between 760 millims. 
and 0‘76 millim. Temp. 15° C. 
Pressure. 
Log. 
Millims. 
decrement. 
760 
0-0499 
748 
0-0501 
582 
0-0501 
567 
0-0498 
484 
0-0499 
428 
0-0500 
42.3 
0-0500 
414 
0-0499 
399 
0-0500 
303 
0-0500 
301 
0-0497 
283 
0-0498 
268 
0-0499 
212 
0-0504 
209 
0-0500 
201 
0-0507 
193 
0-0501 
174 
0-0501 
148 
0-0498 
128 
0-0501 
108 
0-0499 
103 
0-0499 
101 
0-0497 
96 
0-0497 
76 
0-0497 
72 
0-0499 
61 
0-0498 
33 
0-0498 
22 
0-0500 
17 
0-0499 
14 
0-0497 
11 
0-0499 
9 
0-0499 
7 
0-0499 
6 
0-0498 
2 
0-0498 
1*8 
0-0500 
1-5 
0-0498 
1-0 
0-0499 
0-76 
0-0498 
Pressure. 
Time of one 
Millims. 
complete vibration 
744 
10-76 
614 
10-76 
504 
10-76 
314 
10-76 
134 
10-76 
64 
10-76 
29 
10-76 
8 
10-76 
0-6 
10-76 
7-9 M 
10-76 
&c. 
&c. 
