n Copernicus's time, but promulgated and argued in rich
Italian, illustrated by analogy, by experiment, and with cultured wit;
taught not to a few scholars here and there in musty libraries, but
proclaimed in the vernacular to the whole populace with all the energy
and enthusiasm of a recent convert and a master of language! Had a
bombshell been exploded among the fossilized professors it had been less
disturbing.

But there was worse in store for them.

A Dutch optician, Hans Lippershey by name, of Middleburg, had in his
shop a curious toy, rigged up, it is said, by an apprentice, and made
out of a couple of spectacle lenses, whereby, if one looked through it,
the weather-cock of a neighbouring church spire was seen nearer and
upside down.

The tale goes that the Marquis Spinola, happening to call at the shop,
was struck with the toy and bought it. He showed it to Prince Maurice of
Nassau, who thought of using it for military reconnoitring. All this is
trivial. What is important is that some faint and inaccurate echo of
this news found its way to Padua, and into the ears of Galileo.

The seed fell on good soil. All that night he sat up and pondered. He
knew about lenses and magnifying glasses. He had read Kepler's theory of
the eye, and had himself lectured on optics. Could he not hit on the
device and make an instrument capable of bringing the heavenly bodies
nearer? Who knew what marvels he might not so perceive! By morning he
had some schemes ready to try, and one of them was successful.
Singularly enough it was not the same plan as the Dutch optician's, it
was another mode of achieving the same end.

He took an old small organ pipe, jammed a suitably chosen spectacle
glass into either end, one convex the other concave, and behold, he had
the half of a wretchedly bad opera glass capable of magnifying three
times. It was better than the Dutchman's, however; it did not invert.

It is easy to understand the general principle of a telescope. A
general knowledge of the common magnifying glass may be assumed.
Roger Bacon knew about lenses; and the ancients often refer to
them, though usually as burning glasses. The magnifying power of
globes of water must have been noticed soon after the discovery of
glass and the art of working it.

A magnifying glass is most simply thought of as an additional lens
to the eye. The eye has a lens by which ordinary vision is
accomplished