It was Lord Kelvin who, but a few years before the thing
was actually accomplished, declared that aerial navigation was an
impracticable dream, and demonstrated its impracticability by
calculation. However the connection may be brought about, it is as
certain as evidence can make it that solar outbursts are coincident
with terrestial magnetic disturbances, and coincident in such a way as
to make the inference of a causal connection irresistible. The sun is
only a little more than a hundred times its own diameter away from the
earth. Why, then, with the subtle connection between them afforded by
the ether which conveys to us the blinding solar light and the
life-sustaining solar heat, should it be so difficult to believe that
the sun's enormous electric energies find a way to us also? No doubt
the impulse coming from the sun acts upon the earth after the manner
of a touch upon a trigger, releasing energies which are already stored
up in our planet.
But besides the evidence afforded by such occurrences as have been
related of an intimate connection between solar outbreaks and
terrestial magnetic flurries, attended by magnificent auroral
displays, there is another line of proof pointing in the same
direction. Thus, it is known that the sun-spot period, as remarked in
a preceding chapter, coincides in a most remarkable manner with the
periodic fluctuations in the magnetic state of the earth.
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