ying one of the foci _S_ (Fig. 27). We
will suppose that the earth is at point _A_ of its orbit and is being
circled round the sun with uniform velocity. As it is circled round the
sun by the sun's aetherial currents, at the same time its satellite the
moon is being circled round the earth by the electro-magnetic Aether
currents which circulate round that planet. We will represent the orbit of
the moon by part of a smaller circle _D_ _E_ _F_, and suppose the moon to
be at point _D_ of that orbit. The mean distance of the moon from the
earth is about 240,000 miles, so that the diameter of the orbit is 480,000
miles, therefore the circumference of the orbit is 480,000 x 3.1416, which
gives us about 1,500,000 miles.

[Illustration: Fig: 27.]

That distance is traversed in about 28 days, so that the moon's average
velocity in its orbit, as it is circled or pushed round the earth, is
about 2200 miles per hour. While, therefore, the moon is travelling 2200
miles, the earth in its journey round the sun has travelled about 64,800
miles in the same time. So that by the time the moon has travelled half
its orbit, that is, from _D_ to _F_, which would take about 14 days, the
earth has also travelled in its orbit 64,800 x 24 x 14 = 21,772,800
miles, with the result, that instead of the moon arriving at point _F_,
which it would do if the earth were stationary, it really arrives at a
point about 21,772,800 miles in front of that point.

In a similar way, while the moon goes on to describe the other half of
the orbit, the earth still proceeds on its journey, so that at the end
of 14 days it is again 21,772,800 miles further on, with the result,
that the centripetal force (by which the moon is attracted to the earth)
keeps it at the distance of 240,000 miles according to Kepler's Second
Law as explained in Art. 103.

The moon, therefore, completes its orbit about 21,772,800 miles further
on than it would do if the earth were stationary. The effect of this
continual progress of the earth on the moon's orbit as it describes its
orbit round the sun is seen in the diagram. As the moon revolves round
the earth thirteen times in one year, it performs thirteen revolutions
round that planet; but it cannot be said that these orbits are perfect
ellipses, as the earth is ever being circled round its central body, the
sun. Even this diagram does not accurately represent the orbital motion
of the moon through space, as it assumes that the earth