1. Sirius 2. Eta Argus 3. Canopus 4. Alpha Centauri 5. Arcturus 6. Rigel 7. Capella 8. Vega 9. Procyon 10. Betelgeuse 11. Achernar 12. Aldebaran 13. Beta Centauri 14. Alpha Crucis 15. Antares 16. Altair 17. Spica 18. Fomalhaut 19. Beta Crucis 20. Pollux Lastly, Regulus, a bright star in the constellation of the Lion, is also ranked by some astronomers in the first magnitude, while others only admit in this class the first seventeen stars in the above list. These divergences are of no importance. In proportion as the scale of brilliancy or magnitude is descended, the number of the stars contained in each class rapidly increases. The number of second magnitude stars in the heavens is about 65; of the third, about 200; of the fifth, 1,100; and of the sixth magnitude, 3,200. Adding these numbers together, we obtain a few over 5,000 stars of the first six magnitudes, and these comprise very nearly all those that can be seen with the naked eye. The smallness of this number nearly always astonishes those who have not tried to form an exact estimate of the number of stars which shine in the celestial vault on the most favorable nights. The aspect of the multitude of sparkling points which are scattered over the sky makes us disposed to believe that they are innumerable, and to be counted, if not by millions, at all events by hundreds of thousands. This is, nevertheless, an illusion. All observers who have taken the trouble to make an exact enumeration of the stars visible to the naked eye have arrived at a maximum of 3,000 as the mean number which can be observed in every part of the heavens, visible at the same time, at the same place; this, of course, is but half of the entire heavens. Argelander has published an exact catalogue of the stars visible on the horizon of Berlin during the course of the year. This catalogue comprises 3,256 stars. According to Humboldt, there are 4,146 visible on the horizon of Paris in the whole course of the year; and as this number increases in proportion as we approach the Equator, that is to say, in proportion as the double movement of the earth unfolds to us during a year a more extensive portion of the heavens, 4,638 stars are already visible to the naked eye on the horizon of Alexandria. We repeat, the maximum number is comprised between 5,000 and 6,000 stars for the entire heavens, including those seen by the most piercing and most accustomed eyes in the best nights for observation. When the atmosphere is lit up by the moon, or by twilight, or, as happens in the great centres of population, by the illumination of the houses and streets, the lowest magnitude stars are effaced altogether, and the number of those visible is consequently much more limited. We may add in conclusion, that the more the scintillation, the more easy it is to distinguish very faint stars.