Page:A short history of astronomy(1898).djvu/255

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Ch VIII. §§ 152—154]
Telescopic Discoveries

To his rival Christopher Scheiner (chapter vi., §§ 124, 125) belongs the credit of the discovery of bright cloud-like objects on the sun, chiefly visible near its edge, and from their brilliancy named faculae (little torches). Scheiner made also a very extensive series of observations of the motions and appearances of spots.

The study of the surface of the moon was carried on with great care by John Hevel of Danzig (1611–1687), who published in 1647 his Selenographia, or description of the moon, magnificently illustrated by plates engraved as well as drawn by himself. The chief features of the moon—mountains, craters, and the dark spaces then believed to be seas—were systematically described and named, for the most part after corresponding features of our own earth. Hevel's names for the chief mountain ranges, e.g. the Apennines and the Alps, and for the seas, e.g. Mare Serenitatis or Pacific Ocean, have lasted till to-day; but similar names given by him to single mountains and craters have disappeared, and they are now called after various distinguished men of science and philosophers, e.g. Plato and Coppernicus, in accordance with a system introduced by John Baptist Riccioli (1598–1671) in his bulky treatise on astronomy called the New Almagest (1651).

Hevel, who was an indefatigable worker, published two large books on comets, Prodromus Cometicus (1654) and Cometographia (1668), containing the first systematic account of all recorded comets. He constructed also a catalogue of about 1,500 stars, observed on the whole with accuracy rather greater than Tycho's, though still without the use of the telescope; he published in addition an improved set of tables of the sun, and a variety of other calculations and observations.

154. The planets were also watched with interest by a number of observers, who detected at different times bright or dark markings on Jupiter, Mars, and Venus. The two appendages of Saturn which Galilei had discovered in 1610 and had been unable to see two years later (chapter vi., § 123) were seen and described by a number of astronomers under a perplexing variety of appearances, and the mystery was only unravelled, nearly half a century after Galilei's first observation, by the greatest astronomer of this period,