Whether this mode of action has been correctly inferred, matters little;
the lateral vortices follow the law of such a position. The inner vortex
always precedes the central from five to eight days, when ascending in
this latitude, and comes to the meridian after the moon. The outer
vortex, on the contrary, follows the central in its monthly round, and
comes to the meridian before the moon. It will be readily understood
that if the axes of these lateral vortices be produced through the
earth, they will pass through similar vortices in the opposite
hemisphere; but as the greatest latitude of the one, corresponds to the
least latitude of the other, the same calculation will not answer for
both. The same remark applies to the central vortex also.
Thus there are six passages each month over latitude 41d; but as there
are intervals of 3d to 6d between two consecutive passages of the same
vortex, it may happen that an observer in the middle latitude, would
perhaps see nothing of their effects without looking for them. Generally
speaking, they are not only seen, but felt. The time of the passage of
the outer vortex ascending, corresponds so nearly (in 38d of latitude)
at certain times, with the passage of the central vortex descending,
that the two may be considered one if attention is not directed to it.
The orbits of these lateral vortices depend, like that of the central
vortex, on the orbit of the moon for eccentricity, but the longitudes of
the perigee will not correspond with the longitude of the moon's
perigee. This follows from the theory. As the elements of these orbits
are only approximately determined, we shall confine our calculations to
the orbit of the central vortex.