Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of his Time

by Dava Sobel

Clocks were important.

The latitude lines, the parallels, really do stay parallel to each other as they girdle the globe from the Equator to the poles in a series of shrinking concentric rings.

The meridians of longitude go the other way: They loop from the North Pole to the South and back again in great circles of the same size, so they all converge at the ends of the Earth.

The zero-degree parallel of latitude is fixed by the laws of nature, while the zero-degree meridian of longitude shifts like the sands of time.

To learn one’s longitude at sea, one needs to know what time it is aboard ship and also the time at the home port or another place of known longitude—at that very same moment. The two clock times enable the navigator to convert the hour difference into a geographical separation. Since the Earth takes twenty-four hours to complete one full revolution of three hundred sixty degrees, one hour marks one twenty-fourth of a spin, or fifteen degrees.

Every day at sea, when the navigator resets his ship’s clock to local noon when the sun reaches its highest point in the sky, and then consults the home-port clock, every hour’s discrepancy between them translates into another fifteen degrees of longitude.

One degree of longitude equals four minutes of time the world over, but in terms of distance, one degree shrinks from sixty-eight miles at the Equator to virtually nothing at the poles.

In the course of their struggle to find longitude, scientists struck upon other discoveries that changed their view of the universe. These include the first accurate determinations of the weight of the Earth, the distance to the stars, and the speed of light.

English clockmaker John Harrison, a mechanical genius who pioneered the science of portable precision timekeeping, devoted his life to this quest. He accomplished what Newton had feared was impossible: He invented a clock that would carry the true time from the home port, like an eternal flame, to any remote corner of the world.

The moon travels a distance roughly equal to its own width every hour.

light was thought to get from place to place in a twinkling, with no finite velocity that could be measured by man.

Is this mean that only ma could measure it?? Not human??

Roemer used the departures from predicted eclipse times to measure the speed of light for the first time in 1676. (He slightly underestimated the accepted modern value of 300,000 kilometers per second.)

thanks to Galileo’s influence, there was still no good map of the stars and no known route for the moon.

Time is to clock as mind is to brain.

time escapes irretrievably, while we watch.

The clocks of the early sixteenth century weren’t equal to the task. They were neither accurate nor able to run true against the assault of changing temperature on the high seas.

(Multiplying a difference in hours by fifteen degrees gives only an approximation of location; one also needs to divide the number of minutes and seconds by four, to convert the time readings to degrees and minutes of arc.)

Galileo saw that the length of a pendulum determines its rate.

Two years later Huygens published a treatise on its principles, called the Horologium, in which he declared his clock a fit instrument for establishing longitude at sea.

in 1664, Huygens’s clocks sailed to the Cape Verde Islands, in the North Atlantic off the west coast of Africa, and kept good track of the ship’s longitude all the way there and back.

Hooke had already made several memorable names for himself in science. As a biologist studying the microscopic structure of insect parts, bird feathers, and fish scales, he applied the word cell to describe the tiny chambers he discerned in living forms. Hooke was also a surveyor and builder who helped reconstruct the city of London after the great fire of 1666. As a physicist, Hooke had his hand in fathoming the behavior of light, the theory of gravity, the feasibility of steam engines, the cause of earthquakes, and the action of springs. Here, in the coiled contrivance of the balance spring, Hooke clashed with Huygens, claiming the Dutchman had stolen his concept.

This is crazy

A much more humane solution lay in the magnetic compass, which had been invented in the twelfth century and become standard equipment on all ships by this time.

the compass helped sailors find direction when overcast skies obscured the sun by day or the North Star at night.

The method seemingly answered the dream of laying legible longitude lines on the surface of the globe, except that it was incomplete and inaccurate.

In 1714 it came out in book form, under the title A New Method for Discovering the Longitude both at Sea and Land.

“One [method] is by a Watch to keep time exactly. But, by reason of the motion of the Ship, the Variation of Heat and Cold, Wet and Dry, and the Difference of Gravity in different Latitudes, such a watch hath not yet been made.”

The poimt to find the longitude

Half a degree of longitude equals two minutes of time—the maximum allowable mistake over the course of a six-week voyage from England to the Caribbean. An error of only three seconds a day, compounded every day at sea for forty days, adds up to two minutes by journey’s end.

Newton continued to believe that the regular motions of the clockwork universe would prevail in guiding ships at sea.

“A good watch may serve to keep a recconing at Sea for some days and to know the time of a celestial Observ[at]ion: and for this end a good Jewel watch may suffice till a better sort of Watch can be found out. But when the Longitude at sea is once lost, it cannot be found again by any watch.”

“A Table of the Sun rising and Setting in the Latitude of Barrow 53 degrees 18 Minutes; also of difference that should & will be betwixt ye Longpendillom & ye Sun if ye Clock go true.”

Night after night, they marked the clock hour when given stars exited their field of view behind the chimney. From one night to the next, because of the Earth’s rotation, a star should transit exactly 3 minutes, 56 seconds (of solar time) earlier than the previous night.

In comparison, the very finest quality watches being produced anywhere in the world at that time drifted off by about one minute every day.

Where in this small-talking world can I find A longitude with no platitude?