398 PELTIER ON THE CAUSES OF THE 
then diminish in the course of the day proportionally to the 
quantity of vapours which have been disengaged under the oppo- 
site tensions of the earth and of space; and the variations of the 
instrument, if other causes did not concur, would serve to indi- 
cate hygrometric changes. Baron von Humboldt says, in the 
Tableau Physique des Régions Equinoziales, in 4to, 1807, p. 100, 
“In the lower equinoctial regions, from the sea to 200 meters, 
the lower strata of the air are slightly charged with electricity ; 
it is difficult to find signs after ten o’clock in the morning, even 
with Bennet’s electrometer. All the fluid appears to be accu- 
mulated in the clouds, which causes frequent electric explosions, 
which are periodical, generally two hours after the culmination 
of the sun, at the maximum of heat, and when the barometric 
tides are near their minimum. In the valleys of the great rivers, — 
for example in those of the Magdalen, the Rio Negro and the 
Cassiquiaré, the storms are constantly towards midnight. In 
the Andes, the height at which the electric explosions are 
stronger and make more noise is between 1800 and 2000 meters. 
The valleys of Caloto and Popayan are known by the frightful 
frequency of these phenomena.” We quote this passage to show 
that in the regions where the electric phenomena are more con- 
siderable and more numerous, the electrometer indicates nothing ; 
but it will now be understood that this absence of sign arises 
from its being always placed, in these regions, at the centre of a 
sphere of resinous vapours, produced every day by the high 
temperature. 
41. When the atmosphere is thus charged with resinous va- 
pours, it is evident that in raising oneself above the ground 
the instrument is disengaged from these vapours, and that the 
opposition of tension must re-appear; the inferior induction 
again takes its resinous superiority, and the superior induc- 
tion loses it, and becomes vitreous by opposition. In atmo- 
spheric experiments, the number of decimeters or of meters 
which it is necessary to raise an electrometer in order to have an 
equal divergence, is the measure of the resinous vapours existing 
in the upper atmosphere; and if in very dry weather ele- 
vating the electrometer a decimeter is sufficient to obtain a 
divergence of five degrees, and it should be necessary another 
day to raise the same instrument sixteen decimeters to obtain 
the same divergence, the upper atmosphere contains fo 
times more of this elastic vapour. The vitreous induction ©: 
