REFRACTIVE INDEX OF GASES ON TEMPERATURE. 
447 
The results are given in the following table 
Hydrogen put in 21st April, 1902. 
Date. 
Temperature 
of 
tubes. 
Temperature 
of 
manometer. 
Ratio. 
Corrected 
ratio. 
Multiplied by 
1 + -00345i:. 
1 + -OOSSOf. 
1 + -00355/. 
° C. 
= G. 
22 nd April 
11-7 
17-4 
3-010 
3-019 
3-142 
3-143 
3-144 
22 nd „ 
11-7 
17-6 
3-007 
3-016 
3-138 
3-139 
3-141 
23rd „ 
59-7 
18-2 
2-583 
2-588 
3-121 
3-129 
3-137 
24th ,, 
71-0 
19-0 
2-509 
2-515 
3-131 
3-140 
3-149 
25th 
83-5 
19-8 
2-442 
2-447 
3-156 
3-164 
3-172 
26th „ 
89-7 
17-1 
2-406 
2-409 
3-154 
3-165 
3-176 
28th „ 
23-3 
16-3 
2-913 
2-920 
3-155 
3-158 
3-161 
28th „ 
22-65 
16-3 
2-916 
2-923 
3-152 
3-155 
3-158 
29th „ 
33-0 
14-8 
2-821 
2-827 
3-148 
3-153 
3-158 
29th ,, 
32-4 
15-4 
2-822 
2-828 
3-145 
3-149 
3-153 
29th „ 
32-3 
15 - 4 
2-826 
2-832 
3-147 
3-152 
3-157 
30th ,, 
65-8 
15-2 
2-556 
2-560 
3-140 
3-149 
3-158 
30th ,, 
65-5 
15-2 
2-561 
2-565 
3-145 
3-153 
3-161 
1 st jMay 
10-8 
14-5 
3-031 
3 - 038 
3-152 
3-153 
3-154 
1 st „ 
10-9 
14-6 
3-033 
3 - 040 
3-156 
3-157 
3-158 
2 nd „ 
77-5 
14-4 
2-476 
2-479 
3-141 
3-151 
3-161 
3rd „ 
84-1 
15-3 
2-438 
2-441 
3-148 
3-159 
3-170 
3rd „ 
83-2 
15-6 
2-442 
2-445 
3-147 
3-157 
3-167 
5 th „ 
81-7 
13-2 
2-447 
2 - 449 
3-139 
3-149 
3-159 
5 th „ 
10-65 
13-2 
3-042 
3-048 
3-159 
3-161 
3-163 
Mean . 
3.148 
3-154 
3-160 
Greatest variation 
+ -oil 
+ -007 
+ -010 
- -008 
- -005 
- -007 
The results on the 22nd, 23rd, and 24th April are fairly consistent, but ou raising 
the temperature to over 80° the values are distinctly higher. From the 28th 
onwards the agreement is quite satisfactory. I conclude that some impurity (COo) 
had come off at the higher temperature, and after that the composition remained 
constant. The results from the 2Hth onwards give a ratio 
3T54 ± -003 
1 + t (-00350 ± -00003) ■ 
The value of the ratio at 0° for the original hydrogen may be taken as the mean of 
the first two observations on 22nd April. This gives 3-141, The amount of impurity 
is thus 13 in 3141, or 1 part in 240. This would not alter the value of the 
temperature coefficient to the present order of accuracy. I did not think it worth 
while to put in new hydrogen, as the absolute purity could hardly be relied on by 
this method of preparation. 
