Description
Atmospheric electricity abounds in the environment; some traces of it are found less than four feet from the surface of the earth, but on attaining greater height it becomes more apparent. The main concept is that the air above the surface of the earth is usually, during fine weather, positively electrified, or at least that it is positive with respect to the Earth's surface, the Earth's surface being relatively negative. Additionally, the presence of electrical action in the atmosphere, due to the accumulation of enormous static charges of current generated presumably by friction of the air upon itself, can account for the various phenomena of lightning and thunderstorms. Other causes to produce electricity in the atmosphere are, evaporation from the Earth's surface, chemical changes which take place upon the Earth's surface, and the expansion, condensation, and variation of temperature of the atmosphere and of the moisture contained in it.
According to M. Peltier, the terrestrial globe is completely negative, and inter-planetary space positive; the atmosphere itself has no electricity, and is only in a passive state; so that the effects observed are due to the relative influence of these two great stores of electricity. Researchers are disposed to assume that the terrestrial globe possesses, at least on its solid part, an excess of negative electricity, and that it is the same with bodies placed at its surface; but it appears to them to follow, from the various observations made, that the atmosphere itself is positively electrified. This positive electricity evidently arises from the same source as the negative of the globe. It is probable that it is essentially in the aqueous vapors with which the atmosphere is always more or less filled that it resides, rather than in the particles of the air itself; but it does not the less exist in the atmosphere.
The measurements of atmospheric electricity can be seen as measurements of difference of potential between a point of the Earth's surface, and a point somewhere in the air above it. The atmosphere in different regions is often found to be at different local potentials, which differ from that of the earth sometimes even by as much as 3000 Volts within 100 feet (30 m). The electrostatic field and the difference of potential of the earth field according to investigations, is in summer about 60 to 100 volts and in winter 300 to 500 volts per meter of difference in height, a simple calculation gives the result that when such a collector is arranged for example on the ground, and a second one is mounted vertically over it at a distance of 2000 meters and both are connected by a conducting cable, there is a difference in potential in summer of about 2,000,000 volts and in winter even of 6,000,000 volts and more.
In the upper regions of the atmosphere the air is highly rarefied, and conducts like the rarefied gases in Geissler's tubes. The lower air is, when dry, a non-conductor. The upper stratum is believed to be charged with positive electricity, while the Earth's surface is itself negatively charged; the stratum of denser air between acting like the glass of a Leyden jar in keeping the opposite charges separate. The theory of atmospheric electricity explains equally many phenomena; free electricity, which is manifested during thunder-storms, being the cause of the former; and electricity of a lower tension, manifested during a display of the aurora borealis, causing the latter.
The electric atmosphere is the most frequent cause which deters or prevents electrical transmissions. During storms, it is seen that the some apparatus works irregularly, interrupting the passage of strong currents instantaneously, and often produces upon the apparatus in the offices, between metallic points, bright sparks; in telegraphic systems the armatures of the electro-magnets are drawn up with great force, and the wires and other metallic substances about the instruments fused. It is also observed, but more rarely, currents, which continue for a longer or shorter time, that prevent working of communication systems.
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