42 Proceedings of the British Association. 
_ capes to the earth, and rushes along its surface, with the vapor in 
the lower parts of the atmosphere, towards the equator, and is 
again carried back by rising vapor to the poles in constant succes- 
sion, interrupted only in part, by the intense cold of the polar re- 
gions, causing the air to be then comparatively dry. The least 
disturbance then, taking place in the highly charged vapor, (either 
by part of the electricity being drawn off to the earth, or by vapor 
_ diffused from the more temperate regions, or by the accession of 
vapor either more or less charged with electricity,) must cause an 
instantaneous flash to pass through the whole mass of vas by 
ing phenomena, polarity, daily PE acaba and constant 
oscillation of the etic nee 
Mr. Espy read ca to shot that the four fluctuations of the 
barometer which occur daily, are produced entirely by the in- 
creasing and diminishing elasticity of the air due to increasing 
and diminishing temperature. When the sun rises, the air be- 
gins to expand by heat; this expansion of the air, especially of 
that near the surface of the earth, lifts the strata of air above, 
which will produce a reaction, causing the barometer to rise; 
and the greatest rise of the barometer will take place when the 
increase of heat in the lower parts of the atmosphere is the most 
rapid, probably about 9 or 10 A. M. The barometer, from that 
time, will begin to fall; and at the moment when the air is part- 
ing with its heat as fast as it receives it, the barometer will indi- 
cate the exact weight of the atmosphere. The barometer, how- 
ever, will continue to descend on account of the diminished ten- 
sion of the air, and consequent sinking upon itself, as the evening | 
advances; and its greatest depression will be at the moment of 
the most rapid diminution of temperature, which will be about 
4 or 5o’clock. At this moment the barometer will indicate a 
less pressure than the true weight of the atmosphere. The whole 
upper parts of the atmosphere have now acquired a momentum 
downwards, which will cause the barometer to rise above the 
mean, as the motion diminishes, which must have taken place 
some time in the night. This rise will be small, however, com- 
pared with that at 9 or 10 A.M. As the barometer now stands 
above the mean, it must necessarily descend to the mean at the 
