of the
sun's surroundings.

[Sidenote: Corona may influence magnets.]

Now the corona of the sun may be compared to some rare animal which we
only see by paying a visit to some distant land, and may consider
ourselves even then fortunate to get a glimpse of; and it might be thought
that the habits of such an animal are not likely to be of any great
importance in our everyday life. But so far from this being the case in
regard to the corona, it is more than possible that the knowledge of its
changes may be of vital interest to us. I have already said that, as yet,
we have no satisfactory account of the reason why changes in sun-spots
seem to influence changes in our magnets on the earth; but one of the
theories put forward in explanation, and one by no means the least
plausible, is that this influence may come, not from the sun-spots
themselves, but from some other solar phenomenon which varies in sympathy
with them; and in particular that it may come from the corona. These wings
which reach out at sun-spot minimum can be seen to extend a considerable
distance, and there is no reason to suppose that they actually cease at
the point where they become too faint for us to detect them further; they
may extend quite as far as the earth itself and even beyond; and they may
be of such a nature as to influence our magnets. As the earth revolves
round the sun it may sometime plunge into them, to emerge later and pass
above or below them; as again the wings spread themselves at sun-spot
minimum and seem to shrink at maximum, so our magnets may respond by
sympathetic though very small vibrations. Hence it is quite possible that
the corona is directly influencing the magnetic changes on the earth.

[Sidenote: Possible importance of corona.]

But it may be urged that these changes are so slight as to be merely of
scientific interest. That may be true to-day, but who will be bold enough
to say that it will be true to-morrow? If we are thinking of practical
utility alone, we may remember that two great forces of Nature which we
have chained into the service of man, steam and electricity, put forth
originally the most feeble manifestations, which might readily have been
despised as valueless; but by careful attention to proper conditions
results of overwhelming practical importance have been obtained from these
forces, which might have been, and for many centuries were, neglected as
too trivial to be worth attention. Recently the wo