thus extend will be about 48 periods, or 865 years. When a series of
solar eclipses begins, the penumbra of the first will just graze the
earth not far from one of the poles. There will then be, on the average,
11 or 12 partial eclipses of the Sun, each larger than the preceding
one, occurring at regular intervals of one Saros. Then the central line,
whether it be that of a total or annular eclipse, will begin to touch
the Earth, and we shall have a series of 40 or 50 central eclipses. The
central line will strike near one pole in the first part of the series;
in the equatorial regions about the middle of the series, and will leave
the Earth by the other pole at the end. Ten or twelve partial eclipses
will follow, and this particular series will cease."

These facts deserve to be expanded a little.

We have seen that all eclipses may be grouped in a series, and that 18
years or thereabouts is the duration of each series, or Saros cycle. But
these cycles are themselves subject to cycles, so that the Saros itself
passes through a cycle of about 64 Saroses before the conditions under
which any given start was made, come quite round again. Sixty-four times
18 make 1152, so that the duration of a Solar eclipse Great Cycle may be
taken at about 1150 years. The progression of such a series across the
face of the Earth is thus described by Mrs. Todd, who gives a very clear
account of the matter:--

"The advent of a slight partial eclipse near either pole of the Earth
will herald the beginning of the new series. At each succeeding return
conformably to the Saros, the partial eclipse will move a little further
towards the opposite pole, its magnitude gradually increasing for about
200 years, but during all this time only the lunar penumbra will impinge
upon the Earth. But when the true shadow begins to touch, the
obscuration will have become annular or total near the pole where it
first appeared. The eclipse has now acquired a track, which will cross
the Earth slightly farther from that pole every time it returns, for
about 750 years. At the conclusion of this interval, the shadow path
will have reached the opposite pole; the eclipse will then become
partial again, and continue to grow smaller and smaller for about 200
years additional. The series then ceases to exist, its entire duration
having been about 1150 years. The series of "great eclipses" of which
two occurred in 1865 and 1883, while others will happen in 1901, 1919,