Royal Society. 387 
the bright mass of light, whilst with the small brilliancy of a 
wax-light the latter betrays its colour even without optical aids 
of absorption. Only prismatic analysis and the action upon 
uranium glass indicate the presence of the electric light also. 
If the particles at a white heat do not reach each other, the 
spark acquires a spot of interruption, which, however, still shows 
red light besides the true electric light, when the particles pre- 
viously at a white heat have become cooled to redness. The 
basal point of the brush, which retrogrades in proportion to the 
larger field in which the electric light becomes visible, is to be 
compared with the spot of interruption of the spark; the par- 
ticles of the solid body which are here still red-hot may, on 
reaching a greater distance, be completely extinguished, so that 
then the electric light alone prevails. The brush could not be 
coloured by a spirit-flame coloured yellow with chloride of 
sodium held under it, as it then becomes converted into a spark. 
The phenomena of the exhausted tube with mercury indicate the 
modification which the electric light undergoes in media other 
than atmospheric air. 
XLV. Proceedings of Learned Societies. 
ROYAL SOCIETY. 
[Continued from p. 314.] 
March 19, 1857.— Dr. W. A. Miller, V.P., in the Chair. 
— following communications were read :— 
*On the Action of Aqueous Vapour in disturbing the Atmo- 
sphere.” By Thomas Hopkins, Esq. 
In this paper it was maintained that the great disturber of the 
equilibrium of atmospheric pressure is the aqueous vapour which is 
diffused through the gases. These gases, when ascending, cool (say 
5°) through expansion by diminution of incumbent pressure, whilst 
the vapour that is within them cools only 1°; and a consequence is, 
that when a mixed mass ascends, the vapour is condensed by the 
cold of the gases. It is well known that condensation of vapour 
gives out much heat, and this heat warms and expands the gases 
when they are forced to ascend, taking vapour with them; and the 
process being repeated and continued, an ascending current is pro- 
duced in the atmosphere, cloud is formed, the barometer sinks, rain 
falls, and winds blow towards the part. 
This was shown to take place in all latitudes, producing disturb- 
ances great in proportion to the amount of vapour condensed. In 
tropical regions, where the aqueous material is abundant, the dis- 
turbances are great, but take place principally in the higher regions 
of the air. The diminution of atmospheric pressure within the tro- 
pies at the surface of the earth, as measured by the barometer, 
extends over a large surface, but is not great in any one place. In 
202 
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