all change of place is accounted for by motion.' [Startling hypothesis!]
'He then exemplified the conditions by placing some pieces of paper on a
table, and slapping his hand down close to them, thus making them fly
off, which he termed applying the momentum. All motion, he said, is in
the direction of the forces; and atoms seek the centre by "terrestrial
centripetation"--a property which causes universal pressure; but in what
these attributes of pushing and pulling differ from gravitation and
attraction was not expounded. Many of his "truths" were as mystified as
the conundrums of Rabelais; so nothing was made of the motion.'

A favourite subject of paradoxical ideas has been the moon's motion of
rotation. Strangely enough, De Morgan, who knew more about past
paradoxists than any man of his time, seems not to have heard of the
dispute between Keill and Bentley over this matter in 1690. He says,
'there was a dispute on the subject, in 1748, between James Ferguson and
an anonymous opponent; and I think there have been others;' but the
older and more interesting dispute he does not mention. Bentley, who was
no mathematician, pointed out in a lecture certain reasons for believing
that the moon does not turn on her axis, or has no axis on which she
turns. Keill, then only nineteen years old, pointed out that the
arguments used by Bentley proved that the moon does rotate instead of
showing that she does not. (Twenty years later Keill was appointed
Savilian Professor of Astronomy at Oxford. He was the first holder of
that office to teach the Newtonian astronomy.)

In recent times, as most of my readers know, the paradox that the moon
does not rotate has been revived more than once. In 1855 it was
sustained by Mr. Jellinger Symons, one of whose staunchest supporters,
Mr. H. Perigal, had commenced the attack a few years earlier. Of course,
the gist of the argument against the moon's rotation lies in the fact
that the moon always keeps the same face turned towards the earth, or
very nearly so. If she did so exactly, and if her distance from the
earth were constantly the same, then her motion would be exactly the
same as though she were rigidly connected with the earth, and turned
round an axis at the earth. The case may be thus illustrated: Through
the middle of a large orange thrust one short rod vertically, and
another long rod horizontally; thrust the further end of the latter
through a small apple, and now turn the whole af