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146

ASTRONOMIA.

which, as we are assured in the commentary which bears the name of Hipparchus, does little more than represent in verse, with very few variations, the matter contained in the two treatises named above, especially in the latter. The great popularity en­joyed by the production of Aratus (Cum sole et luna semper Aratus erit) must have depended upon the attractions presented by his theme, and cer­tainly not upon the spirit or grace with which that theme was handled. We know .the names of thirty-five Greeks who composed commentaries upon it, and we are acquainted with no less than three translations into Latin verse—one by Cicero, of which fragments only remain ; another by Caesar Germanicus, of which a considerable portion has been preserved ; and a third by Rufus Festus Avienus, which is entire. Virgil borrowed largely from this source in those portions of his Georgics which contain references to the heavenly bodies, and particularly in that section which is devoted to prognostics of the Aveather. There are also valuable Greek scholia ascribed to the younger Theon, but manifestly compounded of materials derived from many different quarters. The work itself is divided into three parts :

J. A description of the constellations, extending to line 454.

2. A short account of the Planets, of the Milky Way, of the Tropical Circles, and of the Equator, followed from v. 559 by a full detail of the stars which rise and set as each sign of the zodiac ap­pears in succession (ffwavaroXa'C).

3. At line 733 commences what is frequently regarded as a separate poem, and placed apart under the title A*o<r?7^e?a, consisting of a collection of the various appearances which enable an ob­server of nature to predict the weather. It will be seen below that the constellations described by Aratus still retain, with a few variations, the names by which he distinguishes them.

In a little tract ascribed to Eratosthenes (fl. b. c. 230), entitled KaracrrepLcr/jioi, probably an abridg­ment of a more complete treatise, in which he details the mythological origin of the constellations, together with the number and place of the stars in each, we find the same forms arranged in the same order as in Aratus, who is followed step by step. The Bird, however, is here termed the Swan ; the Centaur is individualised into Chiron; and the Hair of Berenice appears for the first time, having been introduced by Conon in honour of the sister-wife of Ptolemy Euergetes.

Scientific astronomy commenced at Alexandria in the early part of the third century before our era ; and the first steps were made by Timocharis and Aristyllus, who flourished about b. c. 2,90. They invented the method of determining the places of the fixed stars, by referring them to one of the great circles of the heavens, and for this purpose selected the equator. By them, as we learn from Ptolemy, the right ascension and de­cimation of many stars were observed, among others of Spica in the Virgin, which they found to be 8° from the equinox of autumn.

Hipparchus, about 150 years later, followed up tlie track which they had indicated : his observ­ations extended from b.c. 162 to b. c. 127 ; and, whether we regard the originality, the magnitude, or the importance of his labours, he is well entitled to be regarded as the father of the science. (See Plin. H. N. ii. 26.) In addition to many other

ASTRONOMIA.

services, he first drew up a regular catalogue of the fixed stars, pointing out their position and magnitude, he first delineated accurately the shape of the constellations, and he first discovered the precession of the equinoxes by comparing his own observations with those of Timocharis and Aris­tyllus. It is much to be lamented that all the works of so great a man should have perished, with the exception of a commentary in three books upon the description of the fixed stars by Eudoxus and Aratus ('E^^Tjo'ts t$>v 'Apdrov kcu JZvo*6£ov <poiivofjLsvu>v), the least valuable perhaps of all his productions. We have, however, every reason to believe that the substance of his most valuable ob­servations has been preserved in the Almagest of Ptolemy, which long enjoyed such high fame that all former authors were allowed to sink into oblivion.

The catalogue of the fixed stars by Ptolemy (fl. a. d. 100), contained in the seventh and eighth books of the Almagest and derived in all pro­bability in a great measure from that compiled by Hipparchus, long served as the model for all sub­sequent labours in the same field, and little more than two centuries have elapsed since any attempt was made to supersede it by something more per­fect. It embraces 48 constellations (21 northern, 15 southern, and the 12 signs of the zodiac), com­prising 15 stars of the first magnitude, 45 of the second, 208 of the third, 474 of the fourth, 217 of the fifth, 49 of the sixth, 9 obscure, and 5 nebulous, in all 1022. These are the constella­tions, usually denominated the Old Constellations, to distinguish them from the additions made in modern times, and these we shall consider in re­gular order. The stars are enumerated according to the place which they occupy in the figures, the latitude, longitude, and magnitude of each being specified. In connection with many constellations, several stars are mentioned as apoptywroi, that is, not included within the limits of any one of tho figures ; among those near the Lion he notices the Hair of Berenice, among those near the Eagle the Ant'tnous. The.single stars and small groups to which particular names are assigned, are, A returns, the Lyre, Capella, the Kids, the Eagle, the Hyades, the Pleiades, the Manger, the Asses, Regulus (fiaffiXiffKos), Vindeiniatrix, Spica, Antares, the Hound (he does not give the T\.w&§Sirius),Canopus, and Procyon.

Among our Greek authorities we must not pass over Geminus, whose work 'Etcraycoy^ els to. 3>aivo{j.eva. contains in sixteen chapters an exposi­tion of the most striking facts in Astronomy and Mathematical Geography. We know nothing of him personally; but it has been inferred from his book that he was a native of Rhodes, and that he flourished about B. c. 70, at Rome, or at some place under the same parallel. The second chapter treats of the constellations and of those stars and small clusters distinguished by particular names. The Coma Berenices, which is not included in the 21 northern constellations of Ptolemy, has here an independent place assigned to it; the Foal, or Little Horse, is termed irpoTOf.ity 'lttttov Kaff "itt-7ra/>%oj', which seems to indicate that it was in­troduced by Hipparchus ; in addition to the 15 Southern Constellations of Ptolemy, we find the Stream (xuctis vSaros) issuing from the urn of Aquarius, and the Thyrsus of the Centaur. The sixteenth chapter is particularly interesting and valuable, since it contains a parapegma or calendar

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