grass.” In observing the Sun with a telescope the amateur will soon notice that the surface is far more brilliant in the central parts than round the margin of the disk. Vögel has estimated that immediately inside the edges the brightness does not amount to one seventh that of the centre. The difference is entirely due to the solar atmosphere, which is probably very shallow relatively to the great diameter of the Sun. FOOTNOTES: [9] The Rev. F. Howlett measured this spot on the following day, June 20, and found it 63″ in its largest diameter. He used a small refractor, and projected the Sun’s image on to a screen sufficiently distant for it to have a diameter of 3 feet. [10] On May 13, 1890, at 3^h, I tested the three methods alluded to on a scattered train of small spots, and derived the following measurements of length:— By glass micrometer 76,570 miles. " cross wires 76,610 " " cardboard disk 75,770 " In this comparison I used an excellent 4-inch Cooke refractor, belonging to a friend. [11] The maximum duration of totality, under every favouring circumstance, appears to be about 8 minutes. The great eclipse which occurred on August 18, 1868, maintained the total phase for nearly 6 minutes 50 seconds in the Gulf of Siam. In reference to this eclipse, Dr. Weiss says:—“In the records of ancient eclipses there are to be found only two which may be compared in size with that of August 18, 1868, but none in which the totality lasted so long. The first of these is the eclipse of Thales (28 May, 585 B.C.), which is said to have been the first predicted, and to have terminated a bloody war between the Lydians and the Medes. The second was visible on June 17, 1433, in Scotland, and the time of its occurrence was long remembered by the people of that country as ‘the black hour.’” [12] Carrington found that spots near the equator gave a shorter rotation-period than those far removed from it. This offers an analogy to the spots on Jupiter, which move with greater celerity near the equator, though the rule is not absolute. [13] In 1852 Dawes observed and measured a rotatory motion affecting a spot at the rate of about 17° per day. [14] Lalande, in 1778, asserted that “there are spots of very considerable magnitude, which, reappear in the same physical points of the solar disk.” [15] A spot was visible on June 30, 1889, in 40° South latitude. Its recorded duration was 2 days. This object was observed at the Stonyhurst Observatory and at a station in North America. CHAPTER VI. _THE MOON._ Attractive aspect of the Moon.—Absence of air and water.—Only one Hemisphere visible.—Earthshine.—Telescopic observations of the lunar surface.—Eclipses.—Lunar changes.—Formations.—Plato and other objects described.—Table of Moon’s age and formations near terminator.—Occultations of stars.—Visibility of the new Moon.