The rival of this famous nebula in point of visibility is the well-known spiral in the girdle of Andromeda. On a clear night it can easily be seen with the naked eye near the star Nu Andromedæ, and may readily be, as it has often been, mistaken for a comet. Its discovery must, therefore, have been practically coincident with the beginnings of human observation of the heavens; but special mention of it does not occur before the tenth century of our era. A small telescope will show it fairly well, but it must be admitted that the first view is apt to produce a feeling of disappointment. The observer need not look for anything like the whirling streams of light which are revealed on modern long exposure photographs (Plate XXXI., 1). He will see what Simon Marius so aptly described under the simile of 'the light seen from a great distance through half-transparent horn plates'--a lens-shaped misty light, brightening very rapidly towards a nucleus which seems always on the point of coming to definition but is never defined, and again fading away without traceable boundary into obscurity on every side. The first step towards an explanation of the structure of this curious object was made by Bond in the middle of last century. With the 15-inch refractor of the Cambridge (U.S.A.) Observatory, he detected two dark rifts running lengthwise through the bright matter of the nebula; but it was not till 1887 and 1888 that its true form was revealed by Roberts's photographs. It was then seen to be a gigantic spiral or whirlpool, the rifts noticed by Bond being the lines of separation between the huge whorls of the spiral. Of course, small instruments are powerless to reveal anything of this wonderful structure; still there is an interest in being able to see, however imperfectly, an object which seems to present to our eyes the embodiment of that process by which some assume that our own system may have been shaped. So far as the powers of the best telescopes go, the Andromeda Nebula presents no appearance of stellar constitution. Its spectrum, according to Scheiner, is continuous, which would imply that in spite of appearances it is in reality composed of stars; but Sir William Huggins has seen also bright lines in it. Possibly it may represent a stage intermediate between the stellar and the gaseous. [Illustration: PLATE XXXI. 1. [North.] 2. [North.] Photographs of Spiral Nebulæ. By Dr. Max Wolf. 1. Great Nebula in Andromeda. 2. Spiral in Triangulum (M. 33). ]