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the moon’s orbit, and which increases its velocity. His opponents deny 
that it is necessary to take this into account at all,” and probably they 
did so with very good reason ; for, at the opposite side of the moon’s 
orbit, when represented as nearly a circle round the earth, there of course 
would be the same disturbing influence to act against the now precisely 
opposite direction of the moon’s motion. But, if it had only been kept 
in mind that when the earth is regarded as in motion, the moon’s real path 
is always concave to the sun, this dispute could never have been raised, for 
the simple reason that no tangent to the moon’s orbit could then possibly be 
imagined in the direction of the sun ! 
28. It may be from forgetfulness such as this, and the inadvertent con- 
founding together of real and relative and apparent motions, that (in the 
words of Professor Whewell) “ the Copernican system itself is very complex, 
when it undertakes to account, as the Ptolemaic did, for the inequalities of 
the motions of the sun, moon, and planets ; for,” he adds, “even the moon’s 
motion cannot be conceived without comprehending a scheme more complex 
than the Ptolemaic epicycles and eccentrics in their worst form.” But, be 
that as it may, I now appeal to the actual facts of the moon’s real path and 
her greatly varying velocities, upon the Copernican hypothesis, to establish 
one obvious truth, namely, that if these variations of motion are caused by 
the influence of the sun, the sun’s influence upon the moon is inevitably 
repulsive. 
August 12th, 1864. 
