such vacancies with star-clusters which we have already mentioned.

But the most marvelous of the ``coal-sacks'' are those that have been
found by photography in Sagittarius. One of Barnard's earliest and
most excellent photographs includes two of them, both in the
star-cluster M8. The larger, which is roughly rectangular in outline,
contains one little star, and its smaller neighbor is lune-shaped --
surely a most singular form for such an object. Both are associated
with curious dark lanes running through the clustered stars like
trails in the woods. Along the borders of these lanes the stars are
ranked in parallel rows, and what may be called the bottoms of the
lanes are not entirely dark, but pebbled with faint stellar points.
One of them which skirts the two dark gaps and traverses the cluster
along its greatest diameter is edged with lines of stars, recalling
the alignment of the trees bordering a French highway. This road of
stars cannot be less than many billions of miles in length!

All about the cluster the bed of the Galaxy is strangely disturbed,
and in places nearly denuded, as if its contents had been raked away
to form the immense stack and the smaller accumulations of stars
around it. The well-known ``Trifid Nebula'' is also included in the
field of the photograph, which covers a truly marvelous region, so
intricate in its mingling of nebulæ, star-clusters, star-swarms,
star-streams, and dark vacancies that no description can do it
justice. Yet, chaotic as it appears, there is an unmistakable
suggestion of unity about it, impressing the beholder with the idea
that all the different parts are in some way connected, and have not
been fortuitously thrown together. Miss Agnes M. Clerke made the
striking remark that the dusky lanes in M8 are exemplified on the
largest scale in the great rift dividing the Milky Way, from Cygnus in