rding as their orbits
are of less or greater eccentricity, and this in the ratio of the minor
axis. On the other hand, under the influence of a force acting
centripulsively in the inverse ratio of the square roots of the
distances, we find the mean effect to be as the minor axis of the
ellipse _directly_, so that two planets in orbits of different
eccentricity, but having the same major axis, experience a different
amount from the action of this radial stream, the least eccentric orbit
being that which receives the greatest mean effect. By combining these
two results, we get a ratio of equality; and, consequently, the action
of the radial stream will be the same for the same orbit, whatever
change may take place in the eccentricity, and the mean distance of the
planet will be unchanged. A little consideration will also show that the
effect of the centrifugal momentum due to the density of ether will also
be the same by change of eccentricity; for the positive will always
balance the negative effect at the greatest and least distances of the
planet. The same remark applies to the effect of the tangential current,
so that no change can be produced in the major axes of the planetary
orbits by change of eccentricity, as an effect of the resistance of the
ether.

We will now suppose a planet's orbit to be inclined to the central plane
of the vortex, and in this case, also, we find, that the action of the
radial stream tends to increase the inclination in one quadrant as much
as it diminishes it in the next quadrant, so that no change of
inclination will result. But, if the inclination of the orbit be changed
by planetary perturbations, the mean effect of the radial stream will
also be changed, and this will tell on the major axis of the orbit,
enlarging the orbit when the inclination diminishes, and contracting it
when it increases. The change of inclination, however, must be referred
to the central plane of the vortex. Notwithstanding the perfection of
modern analysis, it is confessed that the recession of the moon's nodes
does yet differ from the theory by its 350th part, and a similar
discrepancy is found for the advance of the perigee.[40] This theory is
yet far too imperfect to say that the action of the ethereal medium will
account for these discrepancies; but it certainly wears a promising
aspect, worthy the notice of astronomers. There are other minute
discordancies between theory and observation in many astronomical