PROPERTIES OF MATTER IN THE GASEOUS STATE. 
743 
This was clearly a point which might be tested even though no very close approxi¬ 
mation should be reached. Hydrogen was accordingly tried. 
Table IY. — Thermal transpiration of hydrogen by meerschaum plate No. 2 ('25 inch 
or 6‘3 millims. thick). Temperature of steam, 212° F. or 100° C.; temperature 
of water, 47° F. or 8° C. 
Mean pressure by 
gauge. 
vacuum 
Difference of press ure by 
siphon gauge. 
Ratio of mean pressure to 
difference of pressure. 
inches. 
millims. 
inch. 
millims. 
30-2 
767 
•88 
23-37 
32-4 
13-0 
330 
•60 
15-24 
21 
7'5 
190-5 
•44 
11-18 
17 
4-25 
107-9 
•28 
711 
15 
2-0 
50-8 
•15 
3-81 
133 
10 
25-4 
•08 
2-03 
12-5 
0-5 
12-7 
■036 
0-91 
13-7 
This table shows that at the pressure of the atmosphere the difference with hydrogen 
was four times as great as it had been with air, and reached the very considerable 
figure of ‘92 of an inch of mercury. This was much more than had been anticipated, 
although there was nothing in the theory to show that it should not exist. This 
great difference at the higher pressures only serves to bring out more forcibly the 
convergence according to Law IY. as the pressure falls. At pressures of 1 inch it will 
be seen that the differences for air and hydrogen are as 12’5 to 20, while if the results 
at *5 inch could be trusted, the ratio is 13*7 to 13*6. 
S) DCOCLXXiX. 
o c 
