The motion of the earth in space can be disproved
by a comparison between the supposed speed of the
earth and that of the other planets, if we base our
considerations on the principle that a body in motion
creates an apparent speed equal to its own, in bodies
it encounters, which is usually demonstrated by the
experiment of a moving vehicle, such as a train. It is
difficult to judge at first sight whether it is the train,
or what can be seen outside which is moving away,
but one fact is certain, i.e. that the two speeds, one of
which is real and the other apparent, are equal. For
this reason, if the earth were in motion, it would
create in the planets and constellations an initial
apparent speed equal to its own. Consequently, there
can be no speed in the heavens lower than that of
the earth’s, since it represents a basic speed from
which the apparent motions would be derived; but
as it can be seen, the displacement of the constellations
and of the planets, with the exception of Mercury
and Venus, is slower than the supposed speed
of the earth, which under the circumstances stated
above, is a material impossibility. It should, moreover,
be considered that the real speeds of the planets
have to be added to the apparent motions created by
the supposed movement of the earth, with the result
that the planets ought to pass before us like a flash...
