OF GASES AT HIGH EXHAUSTIONS. 
427 
exhaustions it introduces errors which interfere with the uniformity of the results. 
A series of experiments were accordingly undertaken to trace the special action of 
aqueous vapour when mixed with air. 
The apparatus as represented in fig. 1 was slightly altered for this purpose, without, 
however, interfering with the parts affecting the measurements. The drying tubes 
of phosphoric anhydride were removed, and a small glass bulb filled with pure water 
was sealed on to the end of the arm p (the arm which, working between metal stops, 
gives motion to the viscosity bulb). The object of attaching the water bulb to this part 
of the apparatus was to allow the aqueous vapour readily to diffuse into the viscosity 
bulb, and drive the unsaturated air before it when the pump was worked. 
The apparatus, thus arranged and full of air at the normal pressure, was left to 
itself for twenty-four hours, to allow aqueous vapour to diffuse through it. The 
temperature was uniformly 15° the whole time. 
Observations were simultaneously taken with the candle flame, so as to measure the 
repidsion due to radiation in the presence of aqueous vapour. 
The results are given in the following table :— 
700. Table VII.—Log. dec. of moist air at pressures from 760 millims. to O'l millim, 
Pressure in 
and lower. Temp. 15° C. 
Log. 
Piepulsion due 
millims. 
decrement. 
to radiation. 
760 
0T124 
o- 
700 
0T109 
o- 
600 
0-1084 
o- 
500 
0-1062 
o- 
400 
0-1040 
o- 
300 
0-1014 
o- 
200 
0-0993 
o- 
100 
0-0955 
o- 
75 
00937 
o- 
50 
0-0903 
o- 
40 
0-0796 
o- 
20 
0-0589 
o- 
16 
0-0531 
o- 
15 
0-0520 
o- 
13 
0-0516 
o- 
11 
0-0511 
o- 
8 
0-0500 
o- 
7 
0-0498 
o- 
5 
0-0499 
o- 
3 
0-0497 
o- 
1* 
0-0497 
o- 
01 
0-0484 
o- 
0-0441 
1- 
0-0432 
1- 
0-0419 
4- 
0-0406 
5- 
0-0390 
9- 
* At about this degree of exhaustion the last drop of liquid water, which for some time had been 
rapidly evaporating, disappeared. 
MDCCCLXXXI. 3 K 
