reason than that, as just said, all the spiral nebulæ possess the same
kind of spectrum, and probably no one would be disposed to regard them
all as outer universes. As we shall see later, the peculiarity of the
spectra of the spiral nebulæ is appealed to in support of a modern
substitute for Laplace's hypothesis.

Finally, without having by any means exhausted the variety exhibited
by the spiral nebulæ, let us turn to the great representative of the
other species, the Orion Nebula. In some ways this is even more
marvelous than the others. The early drawings with the telescope
failed to convey an adequate conception either of its sublimity or of
its complication of structure. It exists in a nebulous region of
space, since photographs show that nearly the whole constellation is
interwoven with faintly luminous coils. To behold the entry of the
great nebula into the field even of a small telescope is a startling
experience which never loses its novelty. As shown by the photographs,
it is an inscrutable chaos of perfectly amazing extent, where spiral
bands, radiating streaks, dense masses, and dark yawning gaps are
strangely intermingled without apparent order. In one place four
conspicuous little stars, better seen in a telescope than in the
photograph on account of the blurring produced by over-exposure, are
suggestively situated in the midst of a dark opening, and no observer
has ever felt any doubt that these stars have been formed from the
substance of the surrounding nebula. There are many other stars
scattered over its expanse which manifestly owe their origin to the
same source. But compare the general appearance of this nebula with
the others that we have studied, and remark the difference. If the
unmistakably spiral nebulæ resemble bursting fly-wheels or grindstones
from whose perimeters torrents of sparks are flying, the Orion Nebula
rather recalls the aspect of a cloud of smoke and fragments produced