Dr. Chowne on the Elastic Force of Aqueous Vapour. 225 
arsenic, sulphur, carbon, tin, zine, iron, lead, silver, gold, &c., on 
the conducting power of pure copper, we have come to the conclusion 
that there is no alloy of copper which conducts electricity better than 
the pure metal. 
May 3.—Sir Benjamin C. Brodie, Bart., President, in the Chair. 
The following communications were read :— 
**On the relations between the Elastic Force of Aqueous Vapour, 
at ordinary temperatures, and its Motive Force in producing Currents 
of Air in Vertical Tubes.” By W. D. Chowne, M.D., F.R.C.P. 
In 1853 the author of this communication made a considerable 
number of experiments which demonstrated that when a tube, open 
at both ends, was placed vertically in the undisturbed atmosphere of 
a closed room, there was an upward movement of the air within the 
tube of sutticient foree to keep an anemometer of light weight in a 
state of constant revolution, though with a variable velocity. An 
abstract of the results of these experiments was printed in the Phi- 
losophical Magazine, vol. xi. p. 227. 
In order to further investigate the immediate cause or nature of 
the force which set the machine in motion, the author instituted a 
series of fresh experiments. 
These experiments were made in the room described in the former 
communication, guarded in the same manner against disturbing 
causes, and with such extra precautions as will be hereafter explained. 
The apparatus used was a tube 96 inches long and 6°75 inches 
uniform diameter, the material zinc. The upper extremity was open 
to its full extent; at the lower, the aperture was a lateral one 
only, into which a piece of zine tube 3 inches in diameter, and bent 
once at right angles, was accurately fitted with the outer orifice 
upward, Within this orifice, which was about 5 inches above the 
level of the floor, an anemometer, described in the former paper, and 
weighing 7 grains, was placed in the horizontal position. About 
midway between the upper and, the lower extremity of the tube, a 
very delicate differential thermometer was firmly and permanently 
fixed, with one bulb outside and the other inside, and the aperture 
through which the latter was inserted completely closed. The scale 
was on the stem of the outer bulb. 
The results of a long series of observations were recorded. The 
state of the dry and the wet bulb of the hygrometer, as well as the 
indications of the differential thermometer, was noted, in connexion 
with the number of revolutions performed per minute by the ane- 
mometer. While the differential thermometer indicated the same 
relative differences between the heat of the atmosphere within and 
without the tube, the velocity of the revolutions was found to vary 
considerably. This variation was discovered to be chiefly, if not 
wholly, dependent on the elasticity of vapour, due to the hygro- 
- metrical state of the atmosphere, as estimated from the dry- and the 
wet-bulb thermometers, and calculated from the tables of Regnault. 
240 observations were recorded and afterwards separated into 
groups, each group comprising those in which the differential ther- 
mometer gave the same indication. 
Phil. Mag. 8. 4, Vol. 21, No. 139, March 1861. Q 
