Another remarkable example of a spiral nebula will be found in M. 51. It is situated in the constellation Canes Venatici, and may be easily picked up, being not far from the end star of the Plough-handle Eta Ursæ Majoris. This strange object, 'gyre on gyre' of fire-mist, was one of the first spirals to have its true character demonstrated by the Rosse telescope. It is visible with moderate optical powers, but displays to them none of that marvellous structure which the great 6-foot mirror revealed for the first time, and which has been amply confirmed by subsequent photographic evidence (Plate XXXII.). [Illustration: PLATE XXXII. Photograph of Whirlpool Nebula (M. 51). Taken by Mr. W. E. Wilson, March 6, 1897.] Among other classes of nebulæ we can only mention the ring and the planetary. Of each of these, one good example can be seen, though, it must be admitted, not much more than seen, with very modest instrumental equipment. Midway between the two stars Beta and Gamma Lyræ, already referred to in connection with the variability of the former, the observer by a little fishing will find the famous Ring Nebula of Lyra. With low powers it appears simply as a hazy oval spot; but it bears magnifying moderately well, and its annular shape comes out fairly with a power of eighty on a 2-1/2 inch, though it can scarcely be called a brilliant object with that aperture, or indeed with anything much under 8 inches. None the less, it is of great interest, the curious symmetry of this gaseous ring making it an almost unique object. It resembles nothing so much as those vortex rings which an expert smoker will sometimes send quivering through the air. Photographs show clearly a star within the ring, and this star has a very curious history, having been frequently visible in comparatively small telescopes, and again, within a year or two, invisible in much larger ones. Photography seems to have succeeded in persuading it to forgo these caprices, though it presents peculiarities of light which are still unexplained. The actinic plate reveals also very clearly that deficiency of light at the ends of the longer diameter of the ring which can be detected, though with more difficulty, by the eye. The class of annular nebulæ is not a large one, and none of its other members come within the effective range of small instruments.