ELECTRIC PHA NOMENA OF THE ATMOSPHERE. 385 
and I thus demonstrate that all the effects observed under a 
serene sky are really owing to the inductions of an electric body, 
and not to the contact of an electrized fluid. 
18. The first care which should be taken in this kind of ex- 
periment, is to assimilate as near as possible to the circumstances 
which accompany the induction of the terrestrial globe, in order 
to have identical results, which could not be obtained if certain 
conditions were neglected. 
One of the first circumstances we must take into account, is 
the infinite smallness of our instruments compared with the size 
of the globe which modifies them by induction. Secondly, their 
elevation above the ground may be regarded as infinitely small, 
and the action of the globe envelops them as a point placed at 
its surface. To approximate to these conditions, we must not 
then place the instrument on a globe, nor even on a plane sur- 
face ; of whatever extent it may be, its limits will always be too 
near to the instrument, and the extreme rays of its induction 
will be far from having the same inclination as those of the ter- 
restrial globe. The instrument, however small it may be, will 
be very much elevated compared with the extent of the surface 
of the body, and its rays will be too nearly vertical. 
19. The experiment may be made in two ways, either by re- 
_ producing the vitreous induction of the celestial space by means 
_ of an insulated globe suspended from the ceiling; or by acting 
“on the surface of an insulated globe resinously electrified. The 
first way is the most simple and easy: we place ourselves 
under this globe with a small electroscope, having a rod of two 
decimeters terminated by a well-polished ball or by a point, 
and under this globe is performed what we should do under a 
serene sky (12-15). Exactly the same results are produced, 
whether with or without radiation. But those persons who are 
prepossessed with the ancient theory, might reproach me with 
materializing the celestial space; with making it a ponderable 
body charged with a special electricity. This would be to re- 
vive the hypotheses of the last century, which made space to be 
a vast receptacle of electricity, from whence the earth was sup- 
plied by means of its conducting vapours. It is to prevent such 
objections that we reproduce the same facts in the way we 
shall now describe, although in reality, for those who are familiar 
with the science of electricity, the preceding experiment is quite 
sufficient. 
