Where Am I? The Sextant Knows
1735 AD
1735 1735
00.02W51.31N
SCI

LONDON, ENGLAND
	When everything is sea in all directions, how do you tell where you are?  That was the problem navigators faced when ships first strayed far from land.
	But in 1735 John Hadley invented a device that let navigators tell their exact latitude (north-south position).  His creation is now called a sextant, Latin for "sixth of a circle," a name taken from its curved shape.
	To use the sextant, the navigator aims it at both the horizon and the sun (or a star at night).  Using the sextant's mirror apparatus, he aligns the two in his sighting telescope.  The scale on the rim of the sextant then shows the altitude of the sun or star above the horizon.
	The navigator can determine his latitude from this because the sun appears lower in the sky toward the Earth's poles and higher toward the equator.
	To tell his longitude (east-west position), he determines the local, or sun-time, then refers to the ship's clock, called a chronometer, which is set to the time in Greenwich, England.  By comparing local time to Greenwich time, he can find his distance east or west of Greenwich.