242 PHYSICS. 
8. Of the Electric Phenomena of the Atmosphere. 
Very soon after the discovery of electricity, attention was called to the 
remarkable similarity of its effects to those of lightning, particularly by 
Gilbert, Grey, Nollet, and Winkler. It was reserved for Benjamin Franklin 
to insist more fully on this identity, and to indicate the experiments by which 
this was to be proved, experiments performed nearly simultaneously by 
himself and others in France and England in 1752. Franklin made use of 
a paper kite with a hempen string, which he held in the hand. This 
apparent child’s play is for certain occasions, as when with a moderate 
wind it is wished to investigate the electricity of the higher strata, even yet 
the simplest and most applicable method. A great advantage is found in 
combining several kites into one system ; nevertheless, in a highly excited 
atmosphere, this experiment becomes very dangerous. Other experimenters 
employed pointed iron rods, supported by insulating glass posts, and either 
standing freely in the air or else attached to some high building; this 
arrangement, however, is only calculated for intense electricity, as the glass 
posts soon lose their insulating property, owing to their becoming coated 
with dust or rain. An electrometer is used to measure the intensity of the 
fluid. Saussure armed the upper end of his electrometer with a wire two 
feet in length: it is still more advantageous to apply a flame to its point (or 
to attach a piece of burning sponge). A very useful piece of apparatus is a 
small Leyden jar of about ten or twelve square inches of inner coating, the 
conductor consisting of a metallic point projecting two inches above the jar, 
on which a metallic wire, of about three feet in length, with spiral turns, is 
attached, and often capable of being removed after charging the jar. 
Traces of electricity are almost always found in the atmosphere, especially 
in clear weather: during a cloudless sky this electricity is always positive. | 
The intensity of electricity in the same place is very variable, and subject to 
a regular oscillation. Feeble at sunrise, it increases until six and seven a.m. 
in summer, eight and nine in autumn and spring, and ten and eleven in 
winter. It then again decreases, reaching its minimum in summer about 
three, and in winter between four and six p.m.; at sunset it again commences 
to ascend, reaching a second maximum about one and a half or two hours 
after. This intensity likewise varies with the season, being greatest in the 
lower strata in January, and least in May, at the time when the air is driest. 
There is the most intimate connexion, as shown by Schibler, between the 
daily and yearly periods of electricity and the variations of relative 
moisture. The intensity of positive electricity is also greater with the 
distance from the surface of the earth, as is shown by even slight differences 
in height. The intensity of electricity is remarkably great during the 
deposit of dew, and in fogs; also when after long continued bad weather it 
clears up suddenly, or when clouds have quickly formed and do not imme- 
diately separate. We sometimes find negative electricity in clouds and 
fogs, but only when rain has fallen from them. All water deposited from 
the air is more or less electric, the electricity being sometimes positive, 
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