parts of the solar surface, and relatively rich streams of particles
will reach it. This, as will be seen from what has been said above, is
in strict accord with the observed variations in the frequency of
auroræ. Even the fact that somewhat fewer auroræ are seen in June than
in December also finds its explanation in the known fact that the
earth is about three million miles nearer the sun in the winter than
in the summer, and the number of particles reaching it will vary, like
the intensity of light, inversely as the square of the distance. These
coincidences are certainly very striking, and they have a cumulative
force. If we accept the theory, it would appear that we ought to
congratulate ourselves that the inclination of the sun's equator is so
slight, for as things stand the earth is never directly over the most
active regions of the sun-spots, and consequently never suffers from
the maximum bombardment of charged particles of which the sun is
capable. Incessant auroral displays, with their undulating draperies,
flitting colors, and marching columns might not be objectionable from
the point of view of picturesqueness, but one magnetic storm of
extreme intensity following closely upon the heels of another, for
months on end, crazing the magnetic needle and continually putting the
telegraph and cable lines out of commission, to say nothing of their
effect upon ``wireless telegraphy'', would hardly add to the charms of
terrestrial existence.

One or two other curious points in connection with Arrhenius'
hypothesis may be mentioned. First, the number of auroræ, according to
his explanation, ought to be greatest in the daytime, when the face of
the earth on the sunward side is directly exposed to the atomic
bombardment. Of course visual observation can give us no information
about this, since the light of the Aurora is never sufficiently
intense to be visible in the presence of daylight, but the records of