440 
PROFESSOR G. G. STOKES OX MR, CROOKES’S EXPERIMENTS OX 
Tables were first formed of the logarithms of — for the different gases for the 
various pressures given by Mr. Crookes down to 0 - 76 millim. The pressures standing 
against equal numbers in these tables for the different gases would be “corresponding” 
pressures. The pressures corresponding to a given number may be obtained from the 
tables by interpolation ; and as the experiments were made at close intervals it 
seemed sufficient to regard only the two adjacent numbers and use proportional parts. 
I do not think it worth while to give these tables at length, but I subjoin a small 
table calculated from them, giving for oxygen, nitrogen, carbonic anhydride, and 
carbonic oxide the pressures corresponding to air pressures decreasing by 100 millims. 
from 760 to 160. It will be seen from Mr. Crookes’s tables that below these 
pressures there is little variation in l until very high exhaustions are reached. 
Hydrogen does not enter into the table, as the highest pressure (760 millims.) in the 
experiments corresponds to a pressure of only about 106 millims. in air. The table 
contains also the logarithms of the ratios of the pressures in the different gases to the 
corresponding pressures in air. 
Corresponding pressures. 
Logs, of ratios to corresponding pressures in air. 
Air. 
O. 
N. 
o 
o 
CO. 
O. 
X. 
C-l 
O 
o 
CO. 
760 
767 - 3 
760-8 
413-3 
760-8 
+ -0042 
+ -0005 
— -2645 
+ *0005 
660 
666-6 
660-9 
359-2 
663-0 
+ -0044 
+ -00i6 
- -2642 
+ -0020 
560 
565 - 5 
559-6 
306-2 
563-8 
+ -0042 
- -0003 
- -2622 
+ -0029 
460 
463-7 
459-0 
250-0 
459-8 
+ -0034 
- -0010 
- -2649 
- -0002 
360 
365"9 
361-6 
194-7 
359"5 
4- -0071 
+ -0019 
- -2669 
- -0006 
260 
263-2 
261-8 
141-9 
258-3 
+ -0053 
+ -0030 
- -2630 
- -0029 
160 
161-2 
159"5 
86-4 
166-7 
+ -0033 
- -0013 
- -2676 
- -0022 
Mean of log-, p'jp . 
+ -0046 
+ *0005 
- -2648 
- -0005 
Number, 
or p'/p. 
1-010 
1-001 
0-540 
0-999 
Log-. (VD'-f-pD), from mean 
•0497 
1-9876 
1-9186 
1-9870 
p’D 1 - 
-pD . . 
1-121 
0-972 
0-829 
0-971 
An inspection of the numbers in the same vertical column in the right-hand portion 
of the above table shows that the logarithm in question is constant as nearly as the 
observations can show. This leads to the following 1 law. 
If any pressure be taken in one gas and the pressures found in other gases for 
which the coefficients of viscosity are as the densities (pressures which have been 
defined as “corresponding”), then if another system of pressures be taken proportional 
to the former the pressures in the new system will also correspond; and consequently 
the ratios of the coefficients of viscosity of the different gases will be the same for the 
pressures in one such system as in another. 
