stupendous sphere rotated once in twenty-four hours, the speed with
which the movement of some of the stars must be executed would be so
portentous as to seem well-nigh impossible. It would, therefore,
seem much simpler on this ground to adopt the other alternative, and
to suppose the diurnal movements were due to the rotation of the
earth. Here Ptolemy saw, or at all events fancied he saw, objections
of the weightiest description. The evidence of the senses appeared
directly to controvert the supposition that this earth is anything
but stationary. Ptolemy might, perhaps, have dismissed this
objection on the ground that the testimony of the senses on such a
matter should be entirely subordinated to the interpretation which
our intelligence would place upon the facts to which the senses
deposed. Another objection, however, appeared to him to possess the
gravest moment. It was argued that if the earth were rotating, there
is nothing to make the air participate in this motion, mankind would
therefore be swept from the earth by the furious blasts which would
arise from the movement of the earth through an atmosphere at rest.
Even if we could imagine that the air were carried round with the
earth, the same would not apply, so thought Ptolemy, to any object
suspended in the air. So long as a bird was perched on a tree, he
might very well be carried onward by the moving earth, but the moment
he took wing, the ground would slip from under him at a frightful
pace, so that when he dropped down again he would find himself at a
distance perhaps ten times as great as that which a carrier-pigeon or
a swallow could have traversed in the same time. Some vague delusion
of this description seems even still to crop up occasionally. I
remember hearing of a proposition for balloon travelling of a very
remarkable kind. The voyager who wanted to reach any other place in
the same latitude was simply to ascend in a balloon, and wait there
till the rotation of the earth conveyed the locality which happened