Routledge History of Philosophy Volume IV

110 SCIENCE AND MATHEMATICS UP TO DESCARTES
general system of mechanics, and gave good licence for Kepler’s laws to be
named as such.
But this was for the future. For the time being popular educated and less
educated interest in the new astronomy was to centre on a more accessible
figure. One of the people to whom Kepler sent a copy of his Mysterium
Cosmographicum was Galileo Galilei. This was natural, for Galileo, then in his
early thirties, was the occupant of the Chair of Mathematics at one of the
foremost scientific centres in Europe, the University of Padua. Galileo replied
immediately, saying how much he was looking forward to perusing it, since he
had been of Copernicus’s opinion for many years. But, remarkably, this
document itself is one of the few pieces of evidence for Galileo’s own opinion
until some thirteen years later, and the change depended upon a new
observational instrument.
It is probably better to think in terms of the emergence of the telescope rather
than its invention, but we may take 1608 as a symbolic year, when the Dutchman
Hans Lippershey presented a spyglass to Prince Maurice, and also applied for a
patent, thereby indicating the passage of the device from the realm of fairground
attraction for producing illusions to that of something potentially useful.
Whoever should be given the prime credit for the invention, the news spread
rapidly, and reached Italy by the following year. Galileo seized on it avidly and
constructed glasses for himself, but in his reports probably exaggerated the
extent to which he had employed optical theory. Then, like Thomas Harriot in
England at almost exactly the same time, he turned his telescope to the skies, but
unlike Harriot he quickly published his findings, in a booklet of 1610 entitled
Sidereus Nuncius.
This caused a sensation, not only because of the new facts themselves, but on
account of their possible implications for rival cosmological systems. We isolate
three discoveries. The first concerns the Moon. The Man in the Moon was, so to
speak, an old friend, and scholastic discussions had frequently touched on the
reason for this feature always pointing towards us. The telescope revealed to
Galileo that the man was far more pock-marked than hitherto thought, and by
observing the changing configuration of the spots he was able plausibly to infer
the existence of shadows caused by mountains and chasms on the Moon’s
surface. This made the Moon more like the Earth, and was a great help in
breaking down the gulf separating the perfect celestial regions from the
imperfect elementary ones, and as such offered indirect support to heliocentric
cosmology.
As regards the fixed stars, Galileo observed far more of them than had been
done previously, and plausibly argued that the Milky Way was composed of stars
too numerous to separate from one another with the naked eye. But a more
important discovery concerned their magnification, for they were not increased
in apparent size as much as would be expected from observation of nearer
objects. Galileo therefore concluded that much of the observed size was to be
attributed not to the body of the star itself, but to twinkle, or, as he called it,