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. This
coincidence runs into the most astonishing details. For instance, when
the sun-spot period shortens, the auroral period shortens to precisely
the same extent; as the short sun-spot periods usually bring the most
intense outbreaks of solar activity, so the corresponding short
auroral periods are attended by the most violent magnetic storms; a
secular period of about two hundred and twenty-two years affecting
sun-spots is said to have its auroral duplicate; a shorter period of
fifty-five and a half years, which some observers believe that they
have discovered appears also to be common to the two phenomena; and
yet another ``superposed'' period of about thirty-five years, which
some investigators aver exists, affects sun-spots and aurora alike. In
short, the coincidences are so numerous and significant that one would
have to throw the doctrine of probability to the winds in order to be
able to reject the conclusion to which they so plainly lead.

But still the question recurs: How is the influence transmitted? Here
Arrhenius comes once more with his hypothesis of negative corpuscles,