ELECTRIC PHA NOMENA OF THE ATMOSPHERE. 383 
manifestation of vitreous electricity, if the instrument be lowered, 
in order to place it again at its first height where the neutral- 
ization took place, the leaves fall again to zero. If we descend 
below this point, by a quantity equal to that which at first sur- 
passed it, the leaves again diverge, but then their sign is con- 
trary, it is resinous. If the instrument be replaced at the point 
of departure, it again falls to zero. Thus, above this point it gives 
a vitreous sign; below it gives a resinous sign; and it again 
becomes neutral by being replaced at the point of departure. 
14, By changing the point of neutralization, that is to say, 
neutralizing the instrument in a stratum above or below the 
first, the signs for the given heights are made to vary. For 
example, in the stratum of air where the instrument diverged 
vitreously it may be made to diverge resinously ; for this it suf- 
fices to neutralize it above this stratum of air, and afterwards to 
lower the instrument to it. In like manner it may be made to 
indicate vitreously in the stratum of air where it had before indi- 
cated resinously ; it will suffice to neutralize it below this stratum, 
then to raise it again to its height. In this experiment the air 
plays no part ; the elevation of the instrument, its depression, 
and its horizontal movement are not able to make it take nor 
to make it lose any electricity; there is a difference in the 
distribution, but not in the quantity ; all takes place as if under 
the induction of an electrified body; all is transitory, nothing 
is permanent. 
I terminated the rod with a large polished ball, in the first 
place to render the phenomenon of induction more intense, and 
to leave no doubt as to the cause; secondly, in order not to 
complicate it with the radiation of electricity accumulated at 
the upper extremity. 
Aipinus had already remarked, in the winter of 1766-67, du- 
ring a frost of 24° R. below zero, and which lasted several weeks, 
that all bodies having lost a great part of their humidity by this 
severe and desiccating cold, they had become insulating, and it 
was sufficient to rub them slightly to obtain bright sparks. 
“ However it may be,” said he, “ the air is not more spontane- 
ously electric during these great frosts than during less degrees 
of cold; by itself it does not give electricity, but bodies take it 
with less friction*.” 
15. Instead of a polished ball, if the rod be provided with a 
* See Guthrie’s Memoir, Trans. Soc. Roy. of Edin., vol. ii, pp- 213-244. 
