zenith always _at exactly the same moment_. She does not appear
under these two conditions simultaneously, except at long
intervals of time. It will be necessary, therefore, to wait for
the moment when her passage in perigee shall coincide with that
in the zenith. Now, by a fortunate circumstance, on the 4th of
December in the ensuing year the moon _will_ present these
two conditions. At midnight she will be in perigee, that is,
at her shortest distance from the earth, and at the same moment
she will be crossing the zenith.

On the _fifth_ question, "At what point in the heavens ought the
cannon to be aimed?"

_Answer._-- The preceding remarks being admitted, the cannon
ought to be pointed to the zenith of the place. Its fire,
therefore, will be perpendicular to the plane of the horizon;
and the projectile will soonest pass beyond the range of the
terrestrial attraction. But, in order that the moon should
reach the zenith of a given place, it is necessary that the
place should not exceed in latitude the declination of the
luminary; in other words, it must be comprised within the
degrees 0@ and 28@ of lat. N. or S. In every other spot the fire
must necessarily be oblique, which would seriously militate
against the success of the experiment.

As to the _sixth_ question, "What place will the moon occupy in
the heavens at the moment of the projectile's departure?"

_Answer._-- At the moment when the projectile shall be discharged
into space, the moon, which travels daily forward 13@ 10' 35'',