REFRACTIVE INDEX OF GASES ON TEMPERATURE. 
443 
The next table gives a complete statement of the values of the ratio 
bands 
pressure 
at different temperatures. 
It is convenient to reduce these values to what they would he if the mercury in 
the manometer was at 0° C. and the tubes of the length at 0° C. 
The coefficient of expansion of brass was taken as 'OOOOID. 
The values of the corrected ratio are given in the fifth column. The next columns 
are the values obtained by multiplying the corrected ratio by the factors (l + '00355^), 
(l + ’00360^) and (l + '00365^) respectively, t being the temperature Centigrade. 
The values are calculated to the nearest 5 in the third decimal place. 
Dry Atmospheric Air. 
Date. 
Temperature 
of 
tubes. 
Temperature 
of 
manometer. 
Ratio. 
Corrected 
Multiplied by 
ratio. 
1+ -00355t 
1 + -00360/. 
1 + -00365/. 
15th Nov. 
° C. 
10-55 
° C. 
13-9 
6-282 
6 - 295 
6-530 
6-535 
6-540 
15 th 
10-65 
14-1 
6-267 
6-280 
6-515 
6-520 
6-525 
22nd 
11-0 
15-8 
6-267 
6-285 
6-530 
6-535 
6-540 
22nd 
11-05 
16-4 
6-262 
6-280 
6 - 525 
6-530 
6-535 
22nd 
11-05 
16-9 
6-270 
6-290 
6-535 
6-540 
6-545 
26 th 
2.3 - 9 
13-6 
6-011 
6 - 025 
6-540 
6-545 
6 - 550 
26th 
24-3 
14-0 
5-989 
6-000 
6-520 
6-525 
6-530 
19th 
48-4 
15-9 
5-551 
5-560 
6-515 
6-530 
6-540 
19th 
52-0 
16-9 
5-499 
5-510 
6-515 
6-530 
6-545 
19th 
52-1 
16-7 
5 - 497 
5-510 
6-515 
6-530 
6-545 
18th 
54-3 
14-4 
5 - 450 
5-460 
6-510 
6-525 
6-540 
18th 
53 - 2 
14-9 
5-482 
5-490 
6-525 
6-540 
6-555 
18th 
53-0 
14-9 
5 - 489 
5 - 495 
6-530 
6-545 
6-560 
21st 
76-5 
18-4 
5-109 
5-120 
6-510 
6-530 
6-550 
21st 
76-1 
18-1 
5-115 
5-125 
6-510 
6-530 
6-550 
25th 
JJ 
100-9 
13-1 
4-788 
4-790 
6 - 505 
6 - 530 
6-555 
Mean. 
Greatest variation. 
6-520 
+ -020 
- -015 
6-535 
+ -010 
- -015 
6 - 545 
+ -015 
- -020 
The superiority of the coefficient ‘00360 is clear from the numbers. The results 
are also shown in the diagram on page 441. Moreover, the agreement between the 
results on the 15th and 22nd shows that no measurable alteration in the gas had 
taken place. 
I think the numbers justify one in taking the ratio as 
6-535 ± -005 
1 + ^ (-00360 ± -00003)' 
The length of each tube was 99‘9 centims. between the inner surfaces of the glass 
plates. 
3 L 2 
