THE SAROS AND THE TOTAL ECLIPSE OF 1806. 685 



passed, the sun will be 28' from the node to the west; and if it is at the descend- 

 ing node, the eclipse will be north of the equator ; for the sun, as it were, has 

 fallen back of the node ; that is, the 223 lunations are completed and the ecHpse 

 occurs before the sun, in his annual course, has got to the node — while he is yet 

 28' back or west of it; and the moon is a little north of the plane of the earth's 

 orbit, which throws its shadow, or the central eclipse, somewhat north of the 

 earth's equator. At the end of the next Saros the sun is another 28' (now nearly 

 a whole degree; back of the node, and the moon's latitude is a little greater, and 

 the eclipse must be still farther north than the other one was. Now the sun's 

 distance from the node being nearly half of a degree greater for every Saros, and 

 the moon's latitude (distance from the plane of ecliptic, or earth's orbit) near 3' 

 more, it follows, that, in the course of time, the sun will be so far from the node 

 and the moon's latitude so great that her shadow and the eclipse will be thrown 

 entirely off, and miss the earth at the north pole. And this occurs when the sun 

 is about 18° from the node and the moon's latitude of 1° 33', which is the ex- 

 treme limit from the node that an eclipse can take place, on account of the 

 moon's orbit separating from the ecliptic plane. Then no more eclipses of this 

 series could strike the earth until the sun had made near the entire circuit of the 

 moon's orbit; that is, to the extreme of eclipse limit on the other side of the same 

 node. And to go this round would require about 12,000 years. Then the pe- 

 numbra of the moon's shadow would begin to touch the earth again at the south 

 pole, and another series of Chaldean periods of eclipses would begin their spiral 

 rounds, or eighteen-year visits to the earth, moving northward at each return, by 

 reason of the sun still approaching the node and the moon's latitude getting less 

 and less until about thirty-six periods have come around, when the sun will again 

 be very near the descending node for this series; the moon (at new, or "change ") 

 be nearly or quite in the ecliptic plane, and her shadow — the eclipse — midway 

 between the poles; then northward as before. But the eclipses at the moon's 

 ascending node first touch the earth at the north pole, and work southward till 

 they finally wear off and leave the earth at the south pole. Now there being 

 more than seventy — well toward eighty — periodical returns of an eclipse during 

 its passage from pole to pole (nearly 8,000 miles), we see that, on an average, each 

 eclipse is about 100 miles farther north or south than the preceding one; and 

 so it is with all the sixty-one solar eclipses that occur during the eighteen years. 

 And so each of the twenty-nine eclipses of the moon that occur in the same time 

 is at first very small, but grows larger (the moon being more deeply immersed in 

 the earth's shadow) at each return, becoming total about the thirteenth return, 

 and continuing so for twenty-two or twenty-three Saroses ; then partial again and 

 growing less and less — but on the opposite side of the earth's shadow — until thir- 

 teen more Saroses have returned; after which the moon, will miss the earth's 

 shadow; and that series of eclipses be no more visible to earth for many centuries. 

 We thus perceive that the Chaldean series of lunar eclipses continues only about 

 forty-eight periods, or 865 years ; whereas the periodic series of solar eclipses 

 last through the long run of about 1,300 years. The moon's ecliptic limit being 



