Let us first consider the stars visible to the naked eye. The number of these down to the sixth magnitude—about the faintest that average eyesight can see—is, for both hemispheres, about 6,000. The number, therefore, visible at _one_ time from any given place is about 3,000. Possibly double this number might be seen by those gifted with exceptionally keen eyesight; but even this is a comparatively small number, scattered as it is over so large an area. Those who do not possess the power of effective enumeration estimate the number visible to the naked eye as considerably greater than is really the case. This is partly due to the irregular distribution of the lucid stars over the celestial vault, and partly to the effect which the aspect of the starry sky produces on the imagination; the fact of the stars increasing in number as they diminish in brightness inducing us to suspect the presence of points of light which we do not actually see. An attempt to count those visible with _certainty_ in any selected portion of the sky will, however, convince any intelligent person that the number, far from being large, is really very small, and that the idea, which some entertain, of a countless multitude is merely an optical illusion, and a popular fallacy which has no foundation in fact. Of course, the number visible in telescopes is very considerable. Perhaps with the largest telescopes 100,000,000 could be seen; but even this large number is very far from being “countless.” The present population of the earth is about 1,400,000,000, or about fourteen times the number of the _visible_ stars! The first thing to be done in studying the heavens with the naked eye is to learn the positions and names of the brighter stars; and from these the fainter ones may easily be identified by means of a star atlas. Those who study the stars in this way have probably a more intimate knowledge of the starry heavens than professional astronomers, who generally find the stars—at least the fainter ones—by referring to a catalogue of stars, and then setting their telescope to the place indicated by the figures given in the catalogue. Although the famous astronomer Sir William Herschel possessed several large telescopes, he also studied the stars with the naked eye, and it is related of this great observer that he could without hesitation identify any star he could see in this way by its name, letter, or number! Such an exhaustive knowledge of the heavens is, of course, very rare; but an acquaintance with all the brighter stars can easily be acquired by any person of ordinary intelligence.