with
its maximum velocity.

At this point, therefore, the eccentricity of the orbit of the moon will
be at its greatest, and, if one revolution could be represented by an
ellipse _E_ _G_ _H_, then that ellipse would be more elongated, and the
difference between the two axes of the moon's orbit would be greater
than at any other point of the earth's orbit.

Thus it can readily be seen that the eccentricity of the moon's orbit is
primarily due to the different velocities of the central body, in this
case the earth, as that body is carried round its central body, the sun.
Where the earth's motion is slowest, there the eccentricity of the
moon's orbit will be at a minimum; but where the earth's velocity is
greatest, there the eccentricity of the moon's orbit will be at a
maximum.

Between this minimum and maximum velocity of the earth in its orbit
there is the constant increase or decrease in the eccentricity of the
orbit of the moon; the eccentricity increasing as the orbital velocity
of the central body increases, and decreasing as the orbital velocity of
the earth decreases. A further fact has, however, to be taken into
consideration, which is that the primary body about which the moon
revolves is itself subject to the same eccentricity of its orbit, and
for similar reasons, as we shall see later on. So that when the
eccentricity of the earth's orbit is at its greatest, then the moon's
orbit will possess its greatest possible eccentricity, and as the
eccentricity of the earth's orbit is dependent upon the orbital velocity
of the sun, so the greatest possible eccentricity of the moon's orbit is
indirectly connected and associated with the sun's motion through space,
which motion will now be considered.

ART. 107. _The Sun and Kepler's First Law._--We have learned in the
previous articles that Kepler's Laws not only apply to planetary motion,
but are equally applicable to the motion of all satellites as they
revolve round their respective planets.

The question now confronts us, as to whether Kepler's Laws are equally
true in their application to the sun? Now the sun is one of the host of
stars that move in the vast infinity of space, and if it can be proved
that Kepler's Laws hold good in relation to one star, as they do in
relation to all planets and satellites, then such a result will have a
most important bearing upon the motions of other stars, and we shall be
able to determine with some degree of exactness wh