principle, its mechanism, and
the method of observing, were most probably explained to him; and we can
believe that an opportunity was afforded him of examining those in
Galileo's observatory, and of perhaps testing their magnifying power
upon some celestial object favourably situated for observation. Though
Milton has not favoured us with any details of his visit to Galileo, yet
it was one which made a lasting impression upon his mind, and was never
afterwards forgotten by him. 'There it was,' he writes, 'I found and
visited the famous Galileo, grown old, a prisoner of the Inquisition for
thinking in astronomy otherwise than the Franciscan and Dominican
licensers thought.' In years long after, when Milton, himself feeble
and blind, sat down to compose his 'Paradise Lost,' the remembrance of
the Tuscan artist and his telescope was still fresh in his memory.

By the invention of the telescope and its application to astronomical
research, a vast amount of information and additional detail have been
learned regarding the bodies which enter into the formation of the solar
system; and by its aid many new ones were also discovered. On sweeping
the heavens with the instrument, the illimitable extent of the sidereal
universe became apparent, and numberless objects of interest were
brought within the range of vision the existence of which had not been
previously imagined.

The Galilean telescope was invented in 1609. But the magnifying power of
certain lenses, and their combination in producing singular visual
effects, are alluded to in the writings of several early authors. The
value of single lenses as an aid to sight had been long known, and
spectacles were in common use in the fourteenth century. Several
mathematicians have described the wonderful optical results obtained
from glasses concave and convex, of parabolic and circular forms, and
from 'perspective glasses,' in which were embodied the principle of the
telescope. It is asserted that our countryman, Roger Bacon (1214), had
some notion of the properties of the telescope; but among those familiar
with the combination of lenses the two men who made the nearest approach
to the invention of the instrument were Baptista Porta and Gerolamo
Fracastro. The latter, who died in 1553, writes as follows: 'For which
reason those things which are seen at the bottom of water appear greater
than those which are at the top; and if anyone look through two
eye-glasses, one placed upon