well worth observing, being marked by singular variations of brilliancy.
Near Arided (the principal star of Cygnus, and now lying due east--some
twenty-five degrees from the zenith) there is seen a straight dark rift,
and near this space is another larger cavity, which has been termed the
northern Coal-sack. The space between [gamma], [delta], and [beta] Cygni
is covered by a large oval mass, exceedingly rich and brilliant. The
neighbouring branch, extending from [epsilon] Cygni, is far less
conspicuous here, but near Sagitta becomes brighter than the other,
which in this neighbourhood suddenly loses its brilliancy and fading
gradually beyond this point becomes invisible near [beta] Ophiuchi.
The continuous stream becomes patchy--in parts very brilliant--where it
crosses Aquila and Clypeus. In this neighbourhood the other stream
reappears, passing over a region very rich in stars. We see now the
greatest extent of the Milky Way, towards this part of its length, ever
visible in our latitudes--just as in spring we see its greatest extent
towards Monoceros and Argo.

[Illustration: PLATE IV.]

I may note here in passing that Sir John Herschel's delineation of the
northern portion of the Milky Way, though a great improvement on the
views given in former works, seems to require revision, and especially
as respects the very remarkable patches and streaks which characterise
the portion extending over Cepheus and Cygnus. It seems to me, also,
that the evidence on which it has been urged that the stars composing
the Milky Way are (on an average) comparable in magnitude to our own
sun, or to stars of the leading magnitudes, is imperfect. I believe, for
instance, that the brilliant oval of milky light in Cygnus comes from
stars intimately associated with the leading stars in that
constellation, and not far removed in space (proportionately) beyond