ELECTRIC PHA NOMENA OF THE ATMOSPHERE. 409 
phenomena which will vary with the conduction of the vapours, 
some producing instantaneous discharges, others exchanges of 
some duration, according to the mass of electricity of the peri- 
phery and the interior conductibility. It is only when the deve- 
lopment of these transformations has been followed, when the 
known laws of electric induction and those resulting from 
changes in temperature shall have been applied to them, that 
we shall be able to form an idea of the igneous phenomena 
which are perceived at such different heights and under such 
different atmospheric aspects. These are subjects to which we 
shall return in future memoirs, when we shall follow in detail the 
connexion of these phznomena, supporting ourselves by nume- 
‘rous facts and by positive experiments. 
_ 57. Rains, like the storms which follow these evaporations, 
are of two kinds, according to the position of the clouds; the 
first is that which arises from the condensation of the inferior 
vapours, which have become vitreous by means of the successive 
eyaporations. These opake vapours, attracted by the terrestrial 
globe, form a stratum of reddish fog, possessing a very powerful 
vitreous tension. On approaching the ground these vapours 
gradually lose this great electric tension, either by radiation or 
by contact with terrestrial bodies, on which they are deposited 
‘under the form of dew*. If they are accumulated into distinct 
clouds, they form below vitreous storms, which discharge them- 
Selves upon the ground by lightning or by sudden local pertur- 
bations of the atmosphere; after these discharges the rain falls 
during some moments, sometimes during several hours, and 
then calm is restored. These kinds of storms are uncommon, 
and are never very intense, neither does the rain last long. The 
proximity of the ground, the density of the air and of the elastic 
vapours of the lower strata, and the agitation of the intermediate 
air,all combine to diminish gradually their vitreous tension, which 
is not the case in the second species of storm. Besides, vitreous 
storms do not affect disagreeably organized bodies; they exagge- 
rate their normal state. The head of man, the summit of plants 
are more resinous by induction, but in fact they possess an elec- 
trie state of the same order as the natural state. After this local 
disturbance it very often happens that fine weather is re-esta- 
* See the observations of Achard in the Nouv. Mém. de l'Acad. Roy. de 
Berlin, 1780, p. 14—23. He has anticipated a part of these facts. 
VOL. III. PART XI. 25 
