Routledge History of Philosophy Volume IV

114 SCIENCE AND MATHEMATICS UP TO DESCARTES
would probably have been no trouble. But Galileo was not content with showing
that the Copernican system was possible: he wanted to show that it actually was
the case. As Salviati says early in the Fourth Day, ‘Up to this point the
indications of [the Earth’s] mobility have been taken from celestial phenomena,
seeing that nothing which takes place on the Earth has been powerful enough to
establish the one position any more than the other.’ He then continued,
Among all sublunary things it is only in the element of water (as something
which is very vast and is not joined and linked with the terrestrial globe as
are all its solid parts, but is rather, because of its fluidity, free and separate
and a law unto itself) that we may recognise some trace or indication of the
Earth’s behaviour in regard to motion and rest. 33
This provided the cue for Salviati to expound, but not in highly developed form,
Galileo’s notorious doctrine of the tides. This, which attributed the tides to a
‘sloshing around’ of the seas caused by the Earth’s twofold motion of translation
and rotation, was based on a phoney argument, even on Galileo’s own terms, and
Galileo should have known it, but apparently genuinely did not.
But historically its main importance is that Galileo thought that he had found a
particularly weighty argument for establishing the Copernican system. To be
sure, it could not be regarded as utterly conclusive, but the statement to that
effect was put at the end of the Day in the mouth of Simplicio, who had been
regularly losing all the arguments.
As to the discourses we have held, and especially this last one concerning
the reasons for the ebbing and flowing of the ocean, I am really not entirely
convinced; but from such feeble ideas of the matter as I have formed, I
admit that your thoughts seem to me more ingenious than many others I
have heard. I do not therefore consider them true and conclusive; indeed,
keeping always before my mind’s eye a most solid doctrine that I once
heard from a most eminent and learned person, and before which one must
fall silent, I know that if asked whether God in His infinite wisdom could
have conferred upon the watery element its observed reciprocating motion
using some other means than moving its containing vessels, both of you
would reply that He could have, and that He would have known how to do
this in many ways which are unthinkable to our minds. From this I
forthwith conclude that, this being so, it would be excessive boldness for
anyone to restrict the Divine power and wisdom to some particular fancy
of his own.
The reference to the Pope was unmistakable, and the offence was heavily
compounded by Salviati’s ironic comment.