he heavens teem with
additional hosts of stars that your unaided vision would never have
given you knowledge of. Any part of the sky may be observed; but, just
to give an illustration, I shall take one special region, namely, that
of the Great Bear (Fig. 1). The seven well-known stars are here shown,
four of which form a sort of oblong, while the other three represent
the tail. I would like you to make this little experiment. On a fine
clear night, count how many stars there are within this oblong; they
are all very faint, but you will be able to see a few, and, with good
sight, and on a clear night, you may see perhaps ten. Next take your
opera-glass and sweep it over the same region; if you will carefully
count the stars it shows, you will find fully two hundred; so that
the opera-glass has, in this part of the sky, revealed nearly twenty
times as many stars as could be seen without its aid. As six thousand
stars can be seen by the eye all over the heavens, we may fairly
expect that twenty times that number--that is to say, one hundred and
twenty thousand stars--could be shown by the opera-glass over the
entire sky. Let us go a step further, and employ a telescope, the
object-glass of which is three inches across. This is a useful
telescope to have, and, if a good one, will show multitudes of
pleasing objects, though an astronomer would not consider it very
powerful. An instrument like this, small enough to be carried in the
hand, has been applied to the task of enumerating the stars in the
northern half of the sky, and three hundred and twenty thousand stars
were counted. Indeed, the actual number that might have been seen with
it is considerably greater, for when the astronomer Argelander made
this memorable investigation he was unable to reckon many of the stars
in localities where they lay very close together. This grand count
only extended to half the sky, and, assuming that the other half is as
richly inlaid with stars, we see that a little telescope like that we
have supposed will, when swept over the heavens, reveal a number of
stars which exceeds that of the population of any city in England
except London. It exhibits more than one hundred times as many stars
as our eyes could possibly reveal. Still, we are only at the beginning
of the count; the very great telescopes add largely to the number.
There are multitudes of stars which in small instruments we cannot
see, but which are distinctly visible from our gre