_Early Observations._—The nebula in Andromeda appears to have been the one first discovered, for the distinguished Persian astronomer Al-Sûfi (who died in 986 A.D.) was undoubtedly acquainted with it. The nebula is figured upon a Dutch map of the stars nearly 400 years old. In 1612 Simon Marius redetected this object, and appropriately likened its appearance to that of a “candle shining through a piece of horn.” In 1618 the nebula in Orion was certainly known, for Cysatus of Lucerne compared it with the head of the fine comet visible in December of that year. Huygens alighted upon the same object in 1656, and appears to have been unconscious of its prior discovery. Only six “nebulæ or lucid spots” were known in 1716, and enumerated by Halley in the ‘Phil. Trans.’ vol. xxix. These included those of Andromeda and Orion. A third was situated in the space between the bow and head of Sagittarius. This is M. 22, and consists of a bright globular cluster of Stars. The fourth was the fine star-group involving ω Centauri, which Halley himself found in 1677. The fifth was another fine group in the right foot of Antinous. This is M. 11, and was discovered by Kirch in 1681. The sixth was the magnificent globular cluster (M. 13) in Hercules, discovered by Halley in 1714. In 1735 the Rev. W. Derham published a list of 16 of these objects, and in 1761 Lacaille summarized 42 nebulæ and star-clusters which he had observed in the southern sky. This was followed by Messier’s tables of 45 nebulæ &c. in 1771, and of 103 in 1781[58]. But these contributions, important though they severally were, sunk into insignificance beside the splendid results obtained by Sir W. Herschel, who during his prolonged and systematic sweeps of the heavens picked up no less than 2500 new nebulæ and clusters which he formed into three catalogues printed in the ‘Phil. Trans.’ as follows:—1786, 1000 objects, 1789, 1000 ditto, 1802, 500 ditto.