FINDING LONGITUDE

We take it for granted now when a location is described as so many degrees latitude and so many degrees longitude, but it wasn't always so simple.

That's the story of Dava Sobel's book Longitude.

Longitude is the story of English clock maker John Harrison, who invented a working chronometer that made the calculation of longitude practical.

Sailors were always capable of sailing by latitude, the imaginary horizontal lines that circle the earth.  Sailors could use celestial navigation to determine their latitude, but longitude presented problems, because longitude is dependent on knowing the time at two separate locations.

The concept of longitude is fairly simple.  A day on earth is twenty-four hours.  If you divide a circle by twenty-four, you arrive at fifteen.  So an hour is equivalent to fifteen degrees.

The problem sailors faced was having a clock or chronometer that was accurate enough to tell them how many hours they were from a designated spot such as a home port.

John Harrison devoted his life to manufacturing an accurate chronometer and his work revolutionized navigation.