mely 18 days before and 18 days after
the Sun's nodal passages); whilst in the case of the Moon, the limits
are the lesser interval of 23 days, being 111/2 on either side of the
Moon's nodal passages.

We have already seen[10] that the Moon's nodes are perpetually
undergoing a change of place. Were it not so, eclipses of the Sun and
Moon would always happen year after year in the same pair of months for
us on the Earth. But the operative effect of the shifting of the nodes
is to displace backwards the eclipse seasons by about 20 days. For
instance in 1899 the eclipse seasons fall in June and December. The
middle of the eclipse seasons for the next succeeding 20 or 30 years
will be found by taking the dates of June 8 and December 2, 1899, and
working the months backwards by the amount of 19-2/3 days for each
succeeding year. Thus the eclipse seasons in 1900 will fall in the
months of May and November; accordingly amongst the eclipses of that
year we shall find eclipses on May 28, June 13, and November 22.

Perhaps it would tend to the more complete elucidation of the facts
stated in the last half dozen pages, if I were to set out in a tabular
form all the eclipses of a succession, say of half a Saros or 9 years,
and thus exhibit by an appeal to the eye directly the grouping of
eclipse seasons the principles of which I have been endeavouring to
define and explain in words.

Approximate
Mid-interval.

1894. March 21. [Symbol: Moon] } March 29. *
April 6. [Symbol: Sun] }

Sept. 15. [Symbol: Moon] } Sept. 22. **
Sept. 29. [Symbol: Sun] }

1895. March 11. [Symbol: Moon] } March 18. *
March 26. [Symbol: Sun] }

Aug. 20. [Symbol: Sun] }
Sept. 4. [Symbol: Moon] } Sept. 4. **
Sept. 18. [Symbol: Sun] }

1896. Feb. 13. [Symbol: Sun] } Feb. 20. *
Feb. 28. [Symbol: Moon] }

Aug. 9. [Symbol: Sun] } Aug. 16. **
Aug. 23. [Symbol: Moon] }

1897. Feb. 1. [Symbol: Sun] Feb. 1. *

July 29. [Symbol: Sun] July 29. **

1898. Jan. 7. [Symbol: Moon] } Jan. 14. *
Jan. 22. [Symbol: Sun] }

July 3. [Symbol: Moon] } July. 10. **
July 18. [Symbol: Sun] }

Dec. 13. [Symbol: Sun] }
Dec. 27. [Symbol: Moon] } Dec. 27. *
1899. Jan. 11. [Symbol: Sun] }

June 8. [Symbol: Sun] } June 15. **
June 23. [Symbol: Moon]