cular velocity of the planet, and, at different
distances, is inversely in the sub-duplicate ratio of those distances.
But the circular velocity of a planet in the same orbit, is in the
simple ratio of the distances inversely. At the perihelion, the planet
therefore moves faster than the ether of the vortex, and at the
aphelion, slower; and the difference is as the square roots of the
distances; but the force of resistance is as the square of the velocity,
and is therefore in the simple ratio of the distances, as we have
already found for the effect of the radial stream, and centrifugal
momentum of the internal ether. At the perihelion this excess of
tangential velocity creates a resistance, which urges the planet towards
the sun, and at the aphelion, the deficiency of tangential velocity
urges the planet from the sun,--the maximum effect being at the apsides
of the orbit, and null at the mean distances. In other positions it is,
therefore, as the cosines of the eccentric anomaly, as in the former
case; but in this last case it is an addititious force at the
perihelion, and an ablatitious force at the aphelion, whereas the first
disturbing force was an ablatitious force at the perihelion, and an
addititious force at the aphelion; therefore, as we must suppose the
planet to be in equilibrium at its mean distance, it is in equilibrium
at all distances. Hence, a planet moving in the central plane of the
vortex, experiences no disturbance from the resistance of the ether.

As the eccentricities of the planetary orbits are continually changing
under the influence of the law of gravitation, we must inquire whether,
under these circumstances, such a change would not produce a permanent
derangement by a change in the mean force of the radial stream, so as to
increase or diminish the mean distance of the planet from the sun. The
law of force deduced from the theory for the radial stream is as the 2.5
power of the distances inversely. But, by dividing this ratio, we may
make the investigation easier; for it is equivalent to two forces, one
being as the squares of the distances, and another as the square roots
of the distances. For the former force, we find that in orbits having
the same major axis the mean effect will be as the minor axis of the
ellipse _inversely_, so that two planets moving in different orbits, but
at the same mean distance, experience a less or greater amount of
centripulsive force from this radial stream, acco