This instrument was vastly improved by the use of a telescope,
which not only allowed fainter objects to be seen, but especially
enabled the sight to be accurately directed to the object
observed.
The instruments of the pre-telescopic age reached their glory in
the hands of Tycho Brahe. He used magnificent instruments of the
simple "pair of compasses" kind--circles, quadrants, and
sextants. These were for the most part ponderous fixed
instruments of little or no use for the purposes of navigation.
But Tycho Brahe's sextant proved the forerunner of the modern
instrument. The general structure is the same; but the vast
improvement of the modern sextant is due, firstly, to the use of
the reflecting mirror, and, secondly, to the use of the telescope
for accurate sighting. These improvements were due to many
scientific men--to William Gascoigne, who first used the
telescope, about 1640; to Robert Hooke, who, in 1660, proposed to
apply it to the quadrant; to Sir Isaac Newton, who designed a
reflecting quadrant;[8] and to John Hadley, who introduced it.
The modern sextant is merely a modification of Newton's or
Badley's quadrant, and its present construction seems to be
perfect.
It therefore became possible accurately to determine the position
of a ship at sea as regarded its latitude. But it was quite
different as regarded the longitude that is, the distance of any
place from a given meridian, eastward or westward.
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