As average stars of the different magnitudes the following may be taken as examples, derived from the Harvard measures: First magnitude, Aldebaran and Spica; second magnitude, β Aurigæ and β Canis Majoris; third magnitude, ι Aurigæ and β Ophiuchi; fourth magnitude, θ Herculis and ε Draconis; and fifth magnitude, ρ Ursæ Majoris and ω Sagittarii. Stars of about the sixth magnitude are, of course, numerous, and lie near the limit of naked-eye vision for average eyesight, although on clear moonless nights still fainter stars may be “glimpsed” by keen-eyed observers. The stars have been divided into groups and constellations, now chiefly used for the purpose of reference, but in ancient times they were associated with the imaginary figures of men and animals, etc. The origin of these constellation figures is doubtful, but they are certainly of great antiquity. Ptolemy’s constellations were 48 in number, but different writers from the First Century B. C. give different numbers, ranging from 43 to 62. Bayer’s _Uranometria_, published in 1603, contains 60, 12 new constellations in the Southern Hemisphere having been added by Theodorus to Ptolemy’s original 48. The figures representing the constellations were originally drawn on spheres, or celestial globes, as they are now called. The ancient astronomers attributed the invention of the sphere to Atlas. It seems certain that a celestial sphere was constructed by Eudoxus in the Fourth Century B. C. Strabo speaks of one made by Krates about the year 130 B. C., and according to Ovid, Archimedes had constructed one at a considerably earlier period. None of these ancient spheres has been preserved. There is, however, in the Vatican a fragment in marble of a Græco-Egyptian planisphere, and a globe in the museum of Arolsen, but these are of much later date. Our knowledge of the original constellation figures is derived from the accounts given by Ptolemy and his successors, and from a few globes which only date back to the Arabian period of astronomy. Among the Arabian globes still existing the most famous is one made of copper, and preserved in the Borgia Museum at Velletri in Italy. It is supposed to have been made by a person called Caisar, who was executed by the Sultan of Egypt in A. D. 1225. The most ancient of all is one discovered some years ago at Florence. It is supposed to date back to A. D. 1081, and to have been made by Meucci. There is also one in the Farnese Museum at Naples, made in A. D. 1225. Of modern celestial globes the oldest is one made by Jansson Blaeu in 1603. This gives all the constellations of the Southern Hemisphere as well as the Northern. Ptolemy’s figures of the constellations were restored by the famous painter Albert Dürer of Nuremberg in 1515. The figures on modern globes and maps have been copied from this restoration. Dürer’s maps are now very rare.