Nearly midway between [beta] and [gamma] lies the wonderful ring-nebula 57 M, of which an imperfect idea will be conveyed by the last figure of Plate 3.  This nebula was discovered in 1772, by Darquier, at Toulouse.  It is seen as a ring of light with very moderate telescopic power.  In a good 3-1/2-inch telescope the nebula exhibits a mottled appearance and a sparkling light.  Larger instruments exhibit a faint light within the ring; and in Lord Rosse’s great Telescope “wisps of stars” are seen within, and faint streaks of light stream from the outer border of the ring.  This nebula has been subjected to spectrum-analysis by Mr. Huggins.  It turns out to be a gaseous nebula!  In fact, ring-nebulae—­of which only seven have been detected—­seem to belong to the same class as the planetary nebulae, all of which exhibit the line-spectrum indicative of gaseity.  The brightest of the three lines seen in the spectrum of the ring-nebula in Lyra presents a rather peculiar appearance, “since it consists,” says Mr. Huggins, “of two bright dots, corresponding to sections of the ring, and between these there is not darkness, but an excessively faint line joining them.  This observation makes it probable that the faint nebulous matter occupying the central portion is similar in constitution to that of the ring.”

The constellation Hercules also contains many very interesting objects.  Let us first inspect a nebula presenting a remarkable contrast with that just described.  I refer to the nebula 13 M, known as Halley’s nebula (Plate 3).  This nebula is visible to the naked eye, and in a good telescope it is a most wonderful object:  “perhaps no one ever saw it for the first time without uttering a shout of wonder.”  It requires a very powerful telescope completely to resolve this fine nebula, but the outlying streamers may be resolved with a good 3-inch telescope.  Sir W. Herschel considered that the number of the stars composing this wonderful object was at least 14,000.  The accepted views respecting nebulae would place this and other clusters far beyond the limits of our sidereal system, and would make the component stars not very unequal (on the average) to our own sun.  It seems to me far more probable, on the contrary, that the cluster belongs to our own system, and that its components are very much smaller than the average of separate stars.  Perhaps the whole mass of the cluster does not exceed that of an average first-magnitude star.

The nebulae 92 M and 50 H may be found, after a little searching, from the positions indicated in the map.  They are both well worthy of study, the former being a very bright globular cluster, the latter a bright and large round nebula.  The spectra of these, as of the great cluster, resemble the solar spectrum, being continuous, though, of course, very much fainter.

The star [delta] Herculis (seen at the bottom of the map) is a wide and easy double—­a beautiful object.  The components, situated as shown in Plate 3, are of the fourth and eighth magnitude, and coloured respectively greenish-white and grape-red.