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 great observatories.  That telescope would be still but a comparatively small one which would show as many stars in the sky as there are people living in the mighty city of London; and with the greatest instruments, the tale of stars has risen to a number far greater than that of the entire population of Great Britain.

In addition to those stars which the largest telescopes show us, there are myriads which make their presence evident in a wholly different way.  It is only in quite recent times that an attempt has been made to develop fully the powers of photography in representing the celestial objects.  On a photographic plate which has been exposed to the sky in a great telescope the stars are recorded by thousands.  Many of these may, of course, be observed with a good telescope,