lly settled that the first telescope was invented
in Holland in 1608; but three men, Hans Lippershey, James Metius,
and Zacharias Jansen, have been given the credit of the invention at
different times. It would seem from certain papers, now in the library
of the University of Leyden, and included in Huygens's papers, that
Lippershey was probably the first to invent a telescope and to
describe his invention. The story is told that Lippershey, who was a
spectacle-maker, stumbled by accident upon the discovery that when
two lenses are held at a certain distance apart, objects at a distance
appear nearer and larger. Having made this discovery, he fitted two
lenses with a tube so as to maintain them at the proper distance, and
thus constructed the first telescope.

It was Galileo, however, as referred to in a preceding chapter, who
first constructed a telescope based on his knowledge of the laws of
refraction. In 1609, having heard that an instrument had been invented,
consisting of two lenses fixed in a tube, whereby objects were made to
appear larger and nearer, he set about constructing such an instrument
that should follow out the known effects of refraction. His first
telescope, made of two lenses fixed in a lead pipe, was soon followed
by others of improved types, Galileo devoting much time and labor to
perfecting lenses and correcting errors. In fact, his work in developing
the instrument was so important that the telescope came gradually to be
known as the "Galilean telescope."

In the construction of his telescope Galileo made use of a convex and
a concave lens; but shortly after this Kepler invented an instrument
in which both the lenses used were convex. This telescope gave a much
larger field of view than the Galilean telescope, but did not give as
clear an image, and in consequence did not come into general use until
the middle of the seventeenth century. The first powerful telescope of
this type was made by Huygens and his brother. It was of twelve feet
focal length, and enabled Huygens to discover a new satellite of Saturn,
and to determine also the true explanation of Saturn's ring.

It was Huygens, together with Malvasia and Auzout, who first applied
the micrometer to the telescope, although the inventor of the first
micrometer was William Gascoigne, of Yorkshire, about 1636. The
micrometer as used in telescopes enables the observer to measure
accurately small angular distances. Before the invention of the