The telescope, ever an ally in the study of the heavens, is in this part of the science absolutely indispensable. In other branches of astronomy we can learn something without its aid. Indeed, many great astronomical discoveries were made long before the telescope was invented. But ere this memorable event in the history of science it was impossible for us to know anything of the existence of the nebulæ. It is indeed true that there is one of these objects which can be just detected by the naked eye. It lies in the constellation of Andromeda, where, on a clear and dark night, a faint spot of light can just be discerned by a good eye. But a mere glimpse gives us really no adequate notion of the true character of the object. It might only, so far as the naked eye discloses its nature, be a cluster of stars like that we have already discerned in Perseus, or like the similar group that, under the name of the Beehive, is comparatively familiar in the constellation of Cancer. With the single exception of the nebula in Andromeda, all the objects so called are entirely telescopic, yet how important a constituent the nebulæ form in the contents of the heavens will be shown by a look at some of the lists of these objects. There are now several thousands of nebulæ known, and their positions in the sky, as well as the details of their appearances, are set forth in the catalogues. The most glorious constellation of stars in the firmament is undoubtedly that of Orion. This splendid group is seen in the south during the winter months, and toward the close of January it is situated in a very convenient position for observing early in the evening. The group is specially characterized by the number of unusually bright stars which it includes, and the three stars in the centre, forming the so-called Belt of Orion, is as well known a celestial figure as the sky contains. Directly under the belt are three much smaller stars nearly in a line, which points straight upward to the middle star of the belt. These three lower stars are usually known as the sword handle of Orion, this being the position which they occupied in the fanciful old sketches of the constellation. The three stars of the sword handle of Orion are plunged in the Great Nebula. This object can not be seen by the unassisted eye, though doubtless around the central star a little haziness is perceptible, and even the slightest telescopic aid will suffice to indicate that the central star of the sword handle is attended by a surrounding glow of light, which renders it quite unlike other stars. This can indeed be sufficiently shown with an ordinary opera-glass, one glance through which will awaken in the beholder a keen desire to study the object under more favorable conditions. But to do justice to the object, telescopes of large power are desirable.