``As a very hot metal emits these
corpuscles,'' says Prof. J. J. Thomson, ``it does not seem an
improbable hypothesis that they are emitted by that very hot body, the
sun.'' Let it be assumed, then, that the sun does emit them; what
happens next? Negatively charged corpuscles, it is known, serve as
nuclei to which particles of matter in the ordinary state are
attracted, and it is probable that those emitted from the sun
immediately pick up loads in this manner and so grow in bulk. If they
grow large enough the gravitation of the sun draws them back, and they
produce a negative charge in the solar atmosphere. But it is probable
that many of the particles do not attain the critical size which,
according to the principles before explained, would enable the
gravitation of the sun to retain them in opposition to the pressure of
the waves of light, and with these particles the light pressure is
dominant. Clouds of them may be supposed to be continually swept away
from the sun into surrounding space, moving mostly in or near the
plane of the solar equator, where the greatest activity, as indicated
by sunspots and related phenomena, is taking place. As they pass
outward into space many of them encounter the earth. If the earth,
like the moon, had no atmosphere the particles would impinge directly
on its surface, giving it a negative electric charge.
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