I am sure it will interest everybody to know that the elements which the stars contain are not altogether different from those of which the earth is made.  It is true there may be substances in the stars of which we know nothing here; but it is certain that many of the most common elements on the earth are present in the most distant bodies.  I shall only mention one, the metal iron.  That useful substance has been found in some of the stars which lie at almost incalculable distances from the earth.

The Nebulae.

In drawing towards the close of these lectures I must say a few words about some dim and mysterious objects to which we have not yet alluded.  They are what are called nebulae, or little clouds; and in one sense they are justly called little, for each of them occupies but a very small spot in the sky as compared with that which would be filled by an ordinary cloud in our air.  The nebulae are, however, objects of the most stupendous proportions.  Were our earth and thousands of millions of bodies quite as big all put together, they would not be nearly so great as one of these nebulae.  Astronomers reckon up the various nebulae by thousands, but I must add that most of them are apparently faint and uninteresting.  A nebula is sometimes liable to be mistaken for a comet.  The comet is, as I have already explained, at once distinguished by the fact that it is moving and changing its appearance from hour to hour, while scores of years elapse without changes in the aspect or position of a nebula.  The most powerful telescopes are employed in observing these faint objects.  I take this opportunity of showing a picture of an instrument suitable for such observations.  It is the great reflector of the Paris Observatory (Fig. 5).

[Illustration:  FIG. 5.  A GREAT REFLECTING TELESCOPE.]

[Illustration:  FIG. 6.  THE RING NEBULA IN LYRA, UNDER DIFFERENT TELESCOPIC POWERS.]

There are such multitudes of nebulae that I can only show a few of the more remarkable kinds.  In Fig. 6 will be seen pictures of a curious object in the constellation of Lyra seen under different telescopic powers.  This is a gigantic ring of luminous gas.  To judge of the size of this ring let us suppose that a railway were laid across it, and the train you entered at one side was not to stop until it reached the other side, how long do you think this journey would require?  I recollect some time ago a picture in Punch which showed a train about to start from London to Brighton, and the guard walking up and down announcing to the passengers the alarming fact that “this train stops nowhere.”  An old gentleman was seen vainly gesticulating out of the window and imploring to be let out ere the frightful journey was commenced.  In the nebular railway the passengers would almost require such a warning.