Marquis Spinola, happening to see this philosophical toy, purchased it,
and presented it to Prince Maurice of Nassau, who imagined it might be
of service for the purpose of military reconnoitring. The value of the
invention was, however, soon realised, and in the following year
telescopes were sold in Paris. In 1609, Galileo, when on a visit to a
friend at Venice, received intelligence of the invention of an
instrument by a Dutch optician which possessed the power of causing
distant objects to appear much nearer than when observed by ordinary
vision. The accuracy of this information was confirmed by letters which
he received from Paris; and this general report, Galileo asserted, was
all he knew of the subject. Fuccarius, in a disparaging letter, says
that one of the Dutch telescopes had been brought to Venice, and that he
himself had seen it. This statement is not incompatible with Galileo's
affirmation that he had not seen the original instrument, and knew no
more about it than what had been communicated to him in the letters from
the French capital. It was insinuated by Fuccarius that Galileo had seen
the telescope at Venice, but, as he denied this, we should not hesitate
to believe in his veracity.

Immediately after his return to Padua, Galileo began to think how he
might be able to contrive an instrument with properties similar to the
one of which he had been informed; and in the following words describes
the process of reasoning by which he arrived at a successful result: 'I
argued in the following manner. The contrivance consists either of one
glass or of more--one is not sufficient, since it must be either convex,
concave, or plane. The last does not produce any sensible alteration in
objects; the concave diminishes them. It is true that the convex
magnifies, but it renders them confused and indistinct; consequently,
one glass is insufficient to produce the desired effect. Proceeding to
consider two glasses, and bearing in mind that the plane causes no
change, I determined that the instrument could not consist of the
combination of a plane glass with either of the other two. I therefore
applied myself to make experiments on combinations of the two other
kinds, and thus obtained that of which I was in search.' Galileo's
telescope consisted of two lenses--one plano-convex, the other
plano-concave, the latter being held next the eye. These he fixed in a
piece of organ pipe, which served the purpose of a tube, the g