e cluster in Hercules.]

And, finally, concerning the nebulae. These mysterious objects exercised
a strong fascination for Herschel, and many are the speculations he
indulges in concerning them. At one time he regards them all as clusters
of stars, and the Milky Way as our cluster; the others he regards as
other universes almost infinitely distant; and he proceeds to gauge and
estimate the shape of our own universe or galaxy of suns, the Milky Way.

Later on, however, he pictures to himself the nebulae as nascent suns:
solar systems before they are formed. Some he thinks have begun to
aggregate, while some are still glowing gas.

[Illustration: FIG. 88.--Old drawing of the Andromeda nebula.]

He likens the heavens to a garden in which there are plants growing in
all manner of different stages: some shooting, some in leaf, some in
flower, some bearing seed, some decaying; and thus at one inspection we
have before us the whole life-history of the plant.

Just so he thinks the heavens contain worlds, some old, some dead, some
young and vigorous, and some in the act of being formed. The nebulae are
these latter, and the nebulous stars are a further stage in the
condensation towards a sun.

And thus, by simple observation, he is led towards something very like
the nebular hypothesis of Laplace; and his position, whether it be true
or false, is substantially the same as is held to-day.

[Illustration: FIG. 89.--The great nebula in Orion.]

We _know_ now that many of the nebulae consist of innumerable isolated
particles and may be spoken of as gas. We know that some are in a state
of whirling motion. We know also that such gas left to itself will
slowly as it cools condense and shrink, so as to form a central solid
nucleus; and also, if it were in whirling motion, that it would send off
rings from itself, and that these rings could break up into planets. In
two familiar cases the ring has not yet thus aggregated into planet or
satellite--the zone of asteroids, and Saturn's ring.

The whole of this could not have been asserted in Herschel's time: for
further information the world had to wait.

These are the problems of modern astronomy--these and many others, which
are the growth of this century, aye, and the growth of the last thirty
or forty, and indeed of the last ten years. Even as I write, new and
very confirmatory discoveries are being announced. The Milky Way _does_
seem to have some affinity with our sun. And