timate which has been made of the general amount of light which we
receive from the stars. According to this estimate the sky is considered
as more or less dark, the combined illumination sent to us by all the
stars being only about the one-hundreth part of what we get from the
full moon.[37]

Secondly, it has been suggested that although light may not suffer any
extinction or diminution from the ether itself, still a great deal of
illumination may be prevented from reaching us through myriads of
extinguished suns, or dark meteoric matter lying about in space. The
idea of such extinguished suns, dark stars in fact, seems however to be
merely founded upon the sole instance of the invisible companion of
Algol; but, as we have seen, there is no proof whatever that it is a
dark body. Again, some astronomers have thought that the dark holes in
the Milky Way, "Coal Sacks," as they are called, are due to masses of
cool, or partially cooled matter, which cuts off the light of the stars
beyond. The most remarkable of these holes is one in the neighbourhood
of the Southern Cross, known as the "Coal Sack in Crux." But Mr. Gore
thinks that the cause of the holes is to be sought for rather in what
Sir William Herschel termed "clustering power," _i.e._ a tendency on the
part of stars to accumulate in certain places, thus leaving others
vacant; and the fact that globular and other clusters are to be found
very near to such holes certainly seems corroborative of this theory. In
summing up the whole question, Professor Newcomb maintains that there
does not appear any evidence of the light from the Milky Way stars,
which are apparently the furthest bodies we see, being intercepted by
dark bodies or dark matter. As far as our telescopes can penetrate, he
holds that we see the stars _just as they are_.

Also, if there did exist an infinite number of stars, one would expect
to find evidence in some direction of an overpoweringly great
force,--the centre of gravity of all these bodies.

It is noticed, too, that although the stars increase in number with
decrease in magnitude, so that as we descend in the scale we find three
times as many stars in each magnitude as in the one immediately above
it, yet this progression does not go on after a while. There is, in
fact, a rapid falling off in numbers below the twelfth magnitude; which
looks as if, at a certain distance from us, the stellar universe were
beginning to _thin out_.

Again, it is