. THE EARTH Annular Fig. 5.—showixg three positions of the shadow-cone. to our own times in the eclipses of 1814, July 17 (total) ; 1843, June 27 (annular) ; 1872, June 6 (annular) ; 1901, May 18 (total) ; the last-mentioned being the ninety-third of the series since that of Nineveh. Between each of these eclipses the lunar perigee— that point in the moon's orbit at which it is nearest to the earth—moves through about 242-4 degrees, so that after three such intervals it has advanced through 727 degrees, and, since 720 degrees is twice round the circle, it is thus only 7 degrees in advance of i
. THE EARTH Annular Fig. 5.—showixg three positions of the shadow-cone. to our own times in the eclipses of 1814, July 17 (total) ; 1843, June 27 (annular) ; 1872, June 6 (annular) ; 1901, May 18 (total) ; the last-mentioned being the ninety-third of the series since that of Nineveh. Between each of these eclipses the lunar perigee— that point in the moon's orbit at which it is nearest to the earth—moves through about 242-4 degrees, so that after three such intervals it has advanced through 727 degrees, and, since 720 degrees is twice round the circle, it is thus only 7 degrees in advance of its original position. For a long period of, say, a thousand years or more, every third eclipse of the series— every one recurring at 3 x 29, 87 years — will therefore be of the same character. Thus those of 1814, 1901, 1988, in the above series are total. The dates mentioned above involve a change from the so-called Old Style to the New. The latter was introduced in 1582, and the formula for conversion from one to the other can be set out in a word or two. To get the New Style from the Old, if the year under consideration comes anywhere— From 1582 to 1699 add 10 days. 1700 ,, 1799 ,, II ,, From iSoo to 1S99 add 12 davs 1900 ,, 2099 ,, 13 ,, Similarly, to change from the New Style to the Old, the days must be subtracted. If a longer view be taken of this twenty-nine-year period, it will be noticed that when it is multiplied by eighteen, the few days short of twenty-nine years amount to practically a whole year, the result being that eighteen times the period is almost exactly 521 years. The consequence of this is that after this lapse of time the eclipses recur on the same day of the year. Thus if we take the Nineveh eclipse of 763 and add 521 a number of times, we get the years 242 , 280, 801, 1322, and 1843 In each of these years, therefore, the eclipse took place on June 15, Old Style, or, using the above formula for 1843, on June 27 in that year
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