the sun is that his surface is flecked
with spots, which appear sometimes in greater numbers and sometimes in
less, and the reason and shape of these spots have greatly exercised
men's minds. Sometimes they are large enough to be seen without a
telescope at all, merely by looking through a piece of smoked or
coloured glass, which cuts off the most overpowering rays. When they are
visible like this they are enormous, large enough to swallow many earths
in their depths. At other times they may be observed by the telescope,
then they may be about five thousand miles across. Sometimes one spot
can be followed by an astronomer as it passes all across the sun,
disappears at the edge, and after a lapse of time comes back again round
the other edge. This first showed men that the sun, like all the
planets, rotated on his axis, and gave them the means of finding out how
long he took in doing so. But the spots showed a most surprising result,
for they took slightly different times in making their journey round the
sun, times which differed according to their position. For instance, a
spot near the equator of the sun took twenty-five days to make the
circuit, while one higher up or lower down took twenty-six days, and one
further out twenty-seven; so that if these spots are, as certainly
believed, actually on the surface, the conclusion is that the sun does
not rotate all in one piece, but that some parts go faster than others.
No one can really explain how this could be, but it is certainly more
easily understood in the case of a body of gas than of a solid body,
when it would be simply impossible to conceive. The spots seem to keep
principally a little north and a little south of the equator; there are
very few actually at it, and none found near the poles, but no reason
for this distribution has been discovered. It has been noted that about
every eleven years the greatest number of spots appears, and that
they become fewer again, mounting up in number to the next eleven years,
and so on. All these curious facts show there is much yet to be solved
about the sun. The spots were supposed for long to be eruptions bursting
up above the surface, but now they are generally held to be deep
depressions like saucers, probably caused by violent tempests, and it is
thought that the inrush of cooler matter from above makes them look
darker than the other parts of the sun's surface. But when we use the
words 'cooler' and 'darker,' we mean onl