's orbit, we are not only
able to demonstrate that the sun satisfactorily fulfils the first and
second of Kepler's Laws, but, conversely, we are able to give a
satisfactory physical explanation of the cause of the eccentricity of
the earth's orbit, which explanation is again primarily to be found in
the universal Aether medium.

ART. 109. _Plane of the Ecliptic and Zodiacal Light._--As already
pointed out, another phenomenon which can be physically accounted for by
the sun's orbital motion through space around its central body, is that
celestial plane known as the Plane of the Ecliptic.

What then is the Plane of the Ecliptic whose physical explanation we are
to attempt? We know that the moon revolves round the earth as the earth
revolves round the sun, while the sun is pursuing its way through space.
It has been found also, that all these motions of these different bodies
take place on one level, so to speak; that is to say, they do not go up
or down in space, but straight on.

So straight do they move, that their path has been likened to the level
of the ocean, on which a ship may sail for thousands of miles, always
keeping the same level and even course. On some such ocean as this in
space all the planetary systems and solar systems seem to move, ever
moving on and on with the same uniformity of level through infinite
space. Further, this plane of the ecliptic is to the celestial sphere
what the sea-level is to the earth. The height of a mountain on the
earth is stated to be so much above the sea-level.

In a similar way astronomers say that a star is a certain height above
the plane of the ecliptic. What then is the physical explanation of this
scientific term? We will lead up to it by first considering the effect
that rotation has upon a liquid body.

It has been demonstrated that if a mass of oil is placed in a
transparent liquid of the same density, so long as the oil is perfectly
at rest, its shape will be that of a sphere which will float about in
the liquid, but as soon as the oil is made to rotate by means of a piece
of wire, then the spherical shape is changed into that of an oblate
spheroid.

Further, the faster it is made to rotate, the more it will bulge out, so
that its equatorial diameter will greatly exceed its polar diameter. The
same principle may be illustrated by making a hoop to revolve rapidly on
its axis, when a similar effect of bulging out will be produced.

Now let us apply this pri