LIST OF IMPORTANT ITEMS IN ASTRONOMICAL PROGRESS.
THE first eclipse recorded occurred at Babylon, March 19, 721 B.C. It was of the moon, and was recorded by Ptolemy. A tablet found at Nineveh is thought to contain a record of a solar eclipse which occurred June 15, 763 B.C.
The earliest-known works on astronomy were prepared by Aristotle about 350 B.C.
The mean motion of the sun and moon was determined by Hipparchus (who also discovered the precession of the equinoxes), 160–125 B.C.
The places and distances of the planets were discovered by Ptolemy, 139–161 A.D.
Astronomy was cultivated by the Arabs about 760 A.D., and introduced into Europe about 1200.
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(Continued from page 8.) The principle of the telescope was described by Roger Bacon in 1250, and in 1537 Leonard Digges arranged lenses so that he could see very distant objects. In 1608 telescopes were constructed by Lipperhey and Jensen. A description of these enabled Galileo, in the following year, to construct an improved instrument, with which, in 1610, he discovered Jupiter's satellites. Kepler's laws of planetary motion were announced in 1609 and 1618. In 1654 Huyghens discovered Saturn's rings. In 1655 Huyghens discovered Titan, the largest of Saturn's satellites. Four more of Saturn's satellites were discovered by Cassius from 1671 to 1684. Wm. Herschel discovered two in 1788; and Bond, the last, in 1848. The reflecting telescope was invented by Gregory in 1663. The first charts of the moon were constructed in 1670. In 1675 Römer discovered the velocity of light by observation of Jupiter's satellites. Newton's system was taught and demonstrated in 1687. In 1705 Halley made the first successful prediction of the return of a certain comet. (This comet, known as Halley's, will return again in 1910.) Uranus was discovered in 1781, and two of his satellites, in 1787, by Herschel; the other two, by Lassell and Struve in 1847. Neptune was found by Dr. Galle, of Berlin, on September 23, 1846, who had been told by Leverrier where the planet would be found. In the following month its satellite was discovered by Mr. Lassell. The art of producing pictures by the action of sunlight upon a sensitized plate (now so extensively used in connection with astronomical work) was discovered by Wedgewood and Davy, of London, in 1802. M. Daguerre improved upon their work, and in 1839 produced Daguerreotype plates. The first photograph of the moon was made by Draper, of New York City, in 1840; but it was not till 1850 and 1851 that good work in this line began to appear. The first picture of the sun was taken in 1845; but successful views of the corona were not secured until 1870. The first photograph of a star was taken in 1850; of a nebula, in 1880; and of a comet, in 1881. Spectrum analysis was applied to astronomy in 1861. In 1877 the two satellites of Mars were discovered by Hall, of Washington. The great Lick Observatory was completed in 1888, and the Yerkes Observatory in 1897. In 1892 the fifth moon of Jupiter was discovered by Prof. E. E. Barnard, at the Lick Observatory. In 1895 Prof. James E. Keeler demonstrated that the rings of Saturn consist of countless satellites revolving about the planet in the same or parallel planes; those at the inner edge moving faster than those at the outer edge. During the same year Professor Barnard discovered a vast nebula in the constellation Scorpio.