tempts have been made to
extend it into regions where we cannot as yet allow that it has earned a
legitimate right of entry. We have heard of the weather and of Indian
famines occurring in cycles identical with the sun-spot cycle; and it is
obvious how tremendously important it would be for us if this were found
to be actually the case. For we might in this way predict years of
possible famine and guard against them; or if we could even partially
foretell the kind of weather likely to occur some years hence, we might
take agricultural measures accordingly. The importance of the connection,
if only it could be established, is no doubt the reason which has misled
investigators into laying undue stress on evidence which will not bear
close scrutiny. For the present we must say decidedly that no case has
been made out for paying serious attention to the influence of sun-spots
on weather. Nevertheless, putting all this aside, there is quite enough of
first-rate importance in the sequel to Schwabe's discovery.

[Sidenote: Greenwich sun records.]

[Sidenote: The sun's rotation.]

Let us review the facts in order. Most of us, though we may not have had
the advantage of seeing an actual sun-spot through a telescope, have seen
drawings or photographs of spots. There is a famous drawing made by James
Nasmyth (of steam-hammer fame), in July, 1864, which is of particular
interest, because at that time Nasmyth was convinced--and he convinced
many others with him--that the solar surface was made up of a
miscellaneous heap of solid bodies in shape like willow leaves, or grains
of rice, thrown together almost at random, and the drawing was made by him
to illustrate this idea. Comparing a modern photograph with it, we see
that there is something to be said for Nasmyth's view, which attracted
much attention at the time and occasioned a somewhat heated controversy.
But since the invention of the spectroscope it has become quite obsolete;
it probably does not correspond in any way to the real facts. But instead
of looking at pictures which have been enlarged to show the detailed
structure in and near a spot, we will look at a series of pictures of
the whole sun taken on successive days at Greenwich in which the spots are
necessarily much smaller, but which show the behaviour of the spots from
day to day. (See Plates X. and XI.) From the date at the foot of each it
will be seen that they gradually cross the disc of the sun (a fact first
di