6th. On the longitude of the perigee of the lunar orbit at the time.

7th. On the moon's true anomaly at the time.


MASS OF THE MOON.

Those elements which represent the moon's distance and motion are
accurately known, and may be taken from the Nautical Almanac, being all
embodied in the moon's parallax or semi-diameter, and in the declination
and right ascension; but for the most important element,--the moon's
mass, we in vain look to astronomy. In fact, it may be averred that the
importance attached to astronomical authority, concerning the mass of
the moon, has caused more trouble than any other question of the whole
theory, until we trusted implicitly to the theory itself to determine
it. The determination of three unknown elements, viz.: the moon's mass,
the inclination of the axis of the vortex, and the right ascension of
that axis, is a more difficult problem than at first sight appears,
owing to the nature of the phenomena, which affords the only clue for
its solution. There are six principal vortices ever in operation on the
surface of the earth, and their disturbing influence extends from 200 to
400 miles. To find the precise centre, by one observer confined to one
place, is difficult; and to separate them, so as to be fully assured
that you have the right one, is perhaps still more so. Happily this
tedious labor is accomplished, and we are able with confidence to give
the following important elements, as very close approximations to the
truth:

Mass of the moon 1/72.3