396 PELTIER ON THE CAUSES OF THE 
possess free electricity ; we are now going to resume these expe- 
riments by placing ourselves in the circumstances which exist — 
in nature in order to obtain the same effects. Two kinds of 
evaporation take place in the atmosphere; that which is effected 
at the surface of water and humid ground, and that which is 
effected when opake clouds return into the state of elastic vapour, 
To imitate the first, I fill a platina capsule with distilled or com- 
mon water, and I place it upon a thermoscopic tripod, insulated 
on cakes of resin, and I connect the tripod with an appropriate 
rheometer; I allow the spontaneous evaporation to continue for 
some time, until the rheometer remains constant during the 
cooling process. I then separate the rheometer in order to in- 
sulate the tripod, and I keep the capsule during a few minutes 
in a rather strong resinous tension. Afterwards, on re-establishing 
the communication with the rheometer, the latter indicates a 
higher degree than that of the spontaneous evaporation ; which 
proves that during the action of resinous electricity the evapo- 
ration has been more considerable. The needle afterwards 
gradually returns to the primitive degree, and thus completes 
the demonstration. The same fact may be verified in another 
manner. The capsule is placed on an insulating body, and a~ 
body charged with vitreous electricity is suspended above it; 
under the induction of this body the water of the capsule quickly 
becomes vitreous, which indicates that the vapour which rises 
from it is resinous, and that it is the material vehicle which car- 
ries to the vitreous body the contrary tension by which it is neu- 
tralized. The vitreous tension of the water is so great that it 
must not be examined without a proof plane, for if the electro- 
scope were brought into immediate contact, the gold leaves might 
be destroyed by it. 
' 38. I have recently made an electric hygrometer, founded on 
the proportionality which exists between the loss of electricity 
and the quantity of vapours contained in the atmosphere: I shall 
elsewhere give a description of it. 1 will merely state, to ren- 
der the experiment to which I am about to refer intelligible, 
that it is nothing else than my index electrometer surmounted 
by a metallic tuft, to which a constant charge of electricity is 
given. I exposed this hygremeter in the open air upon a very 
elevated place; Saussure’s hygrometer indicated 75°, vapours 
disturbed the aspect of the sky, and it was necessary to raise 
the electrometer one meter to have a divergence, which was ob- 
