in their formation. On the other hand, we find (in the Pleiades)
wisps and streamers of nebulous matter clinging about great clusters of
stars, suggesting that they are material left over when these clustered
worlds crystallised out of some vast nebula; and enormous stretches of
nebulous material covering regions (as in Perseus) where the stars are
as thick as grains of silver. More important still, we find a type of
cosmic body which seems intermediate between the star and the nebula.
It is a more or less imperfectly condensed star, surrounded by nebular
masses. But one of the most instructive links of all is that at times a
nebula is formed from a star, and a recent case of this character may be
briefly described.

In February, 1901, a new star appeared in the constellation Perseus.
Knowing what a star is, the reader will have some dim conception of the
portentous blaze that lit up that remote region of space (at least 600
billion miles away) when he learns that the light of this star increased
4000-fold in twenty-eight hours. It reached a brilliance 8000 times
greater than that of the sun. Telescopes and spectroscopes were turned
on it from all parts of the earth, and the spectroscope showed that
masses of glowing hydrogen were rushing out from it at a rate of nearly
a thousand miles a second. Its light gradually flickered and
fell, however, and the star sank back into insignificance. But the
photographic plate now revealed a new and most instructive feature.
Before the end of the year there was a nebula, of enormous extent,
spreading out on both sides from the centre of the eruption. It was
suggested at the time that the bursting of a star may merely have lit up
a previously dark nebula, but the spectroscope does not support this. A
dim star had dissolved, wholly or partially, into a nebula, as a result
of some mighty cataclysm. What the nature of the catastrophe was we will
inquire presently.

These are a few of the actual connections that we find between stars and
nebulae. Probably, however, the consideration that weighs most with
the astronomer is that the condensation of such a loose, far-stretched
expanse of matter affords an admirable explanation of the enormous heat
of the stars. Until recently there was no other conceivable source that
would supply the sun's tremendous outpour of energy for tens of millions
of years except the compression of its substance. It is true that the
discovery of radio-activity ha