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KF5JRV > TECH 15.10.16 12:37l 197 Lines 14073 Bytes #999 (0) @ WW
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Subj: JOHN HARRISON'S TIMEPIECE
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JOHN HARRISON'S TIMEPIECE
An urgent petition reached Parliament on March 25, 1714. Certain "Captains of Her Majesty's
Ships, Merchants of London, and Commanders of Merchant-men" wanted something done
about the day's most pressing problem in navigation, the problem of longitude.
If the elder Cassini thought he had solved the problem with those moons of Jupiter, he
should have heard the profanity and obscenities being uttered on the waterfront or on
any of the ships at sea. Those long, heavy telescopes and cumbersome pendulum
clocks might be all right for some astronomer in Paris, but no seaman could use them
to track and time a tiny Jovian moon from the rolling, tossing deck of a ship. There had
to be a better way of finding longitude at sea.
Until there was, ships could never be sure of their positions east or west of home port
or anywhere else. They could never be sure if they were a few kilometers or many
kilometers from a particular landfall, which would, in either case, probably not be very
well mapped, also because of the longitude problem. Neither the explorers who found
a place nor the cartographers who put it on the map, having themselves had only a
rough idea of longitude, could have ever known exactly the position of the place. Thus,
as long as the problem of longitude at sea defied solution, both navigation and
cartography suffered.
What affected the navy and maritime trade was no trifling matter to Englishmen. So
Parliament voted to offer a reward "for such person or persons as shall discover the
Longitude." The offer: L10,000 for any method capable of determining a ship's
longitude within one degree; L15,000, within 40'; and L20,000, within half of one
degree. A permanent board of examiners, composed of scientists and admirals, was
given responsibility for evaluation proposals and judging the results of accuracy
tests. This became known as the Board of Longitude.
Since dead reckoning, magnetic declination, and Jovian satellites had been
discarded, and the lunar method remained an uncertain prospect, there seemed to
be only one other possible approach - a highly accurate mechanical clock to be
carried on ship. The clock would keep the time of the prime meridian, whether at
Greenwich or Ferro or Paris. By comparing this time with the local time at sea or
on some distant shore, it would be possible to know one's longitude relative to
the prime meridian.
A superior clock just might be the solution, though as the eminent Isaac Newton, by
then the president of the Royal Society, said in 1714. But its invention would not
be easy. Appearing before a Parliamentary committee convened to consider the
longitude petition, Newton said: "...by reason of the Motion of a Ship, the Variation
of Heat and Cold, Wet and Dry, and the Difference of Gravity in Different Latitudes,
such a Watch hath never been made."
Could it ever by? This was the challenge that preoccupied a man named John
Harrison for nearly all his working life.
Harrison was twenty-one years old when Parliament announced the prize. He was
born in 1693 at Foulby in Yorkshire, the eldest son of a poor carpenter. An attack of
smallpox at the age of six may have been decisive in shaping his life. While
convalescing, he became fascinated by a watch his parents, seeking to amuse him,
had laid on his pillow. He never forgot that watch.
In subsequent years young Harrison learned his father's trade, earned some extra
money surveying land, and in the evenings read lectures on mechanics and physics.
By 1714, he had learned to make and repair clocks, first as a sideline, then as his
full-time trade. The more he worked with clocks, the more he applied his emerging
inventive genius to improving the way they were built.
For one thing, Harrison decided that pendulums could be improved upon. They were
made of iron or steel rods, which contracted in the winter, making the clocks run fast,
and expanded in the summer, causing the clocks to lose time. Harrison all but
eliminated this fault with the invention of a pendulum resembling gridiron. It consisted
of nine alternating steel and brass rods, so assembled that the different expansion
and contraction rates of the two metals canceled each other out.
Another of Harrison's inventions was the "grasshopper" escapement, a new type of
control device for the step-by-step release of a clock's driving power. His escapement
was almost frictionless and required no oiling; it thus pointed the way to further
improvements in clockmaking.
In 1728, when he was thirty-five years old, this self-taught country clockmaker felt
himself ready to enter the longitude competition. Harrison packed full-scale models
of the gridiron pendulum and the grasshopper escapement, to show what he had done,
and the drawings for the proposed marine clock, to show what he planned to do, and
went to London in search of financial assistance. It was suggested that he visit George
Graham, the country's foremost horologist. Graham must have been impressed by
Harrison. He loaned Harrison money out of his own pocket and advised him to return
home and build the marine clock he proposed. Harrison, a methodical man and
something of a perfectionist, spent the next seven years building his "Number One",
as it was later called.
Harrison's clock was finished in 1735. Large and heavy, standing almost one meter
tall, it was no thing of beauty. Harrison had eliminated as many moving parts as possible.
Instead of using a pendulum, which had proven unreliable at sea, he designed a system of
two large brass balances connected by wires. The motions of the two balances, of equal
weight, were always opposed so that the effect of a roll of a ship on one would be
counteracted by the other. A committee of the Royal Society, after examining the clock's
mechanism, decided that tit was sufficiently promising to be worthy of a trial at sea.
There is no record of how well the clock performed on the voyage, in 1736, to Lisbon.
George Proctor, captain of the Centurian, probably reflecting the seaman's skeptical
attitude toward new-fangled instruments, wrote, "the Difficulty of measuring Time truly,
where so many unequal Shocks and Motions stand in Opposition to it, gives me concern
for this honest Man and makes me feel he has attempted Impossibilities." On the return
trip, aboard the Oxford, Harrison seems to have made a more favorable impression.
Relying on his clock, he estimated the ship's position to be one and a half degrees west
of the dead-reckoning calculations. He was proved right on landfall.
Even so, the voyage to Lisbon and back was made along a well-known trade route
following a roughly north-south course, which was hardly a definitive test of the clock.
Harrison received a subsidy from the board and went home again to build Number Two.
But when it was completed England was at war with Spain, and the Admiralty, fearing that
the clock might fall into enemy hands, vetoed a sea trial.
Harrison retired to work on yet another version, Number Three, which took him seventeen
years to build. Then, without even offering it for sea trial, he turned to the construction of
Number Four. The first three were all heavy, boxlike instruments, but not Number Four. It
was more like a large pocket watch, about twelve centimeters in diameter, with a jeweled
mechanism that was the product of years of exquisite craftsmanship. Into the clock had
gone "fifty years of self-denial, unremitting toil, and ceaseless concentration," Harrison
said, but he was finally confident that the prize was within grasp. "I think I may make
bold to say," Harrison wrote, "that there is neither any other Mechanism or Mathematical
thing in the World that is more beautiful or curious in texture than this my watch or T
ime-keeper for the Longitude."
A sea trial for Number Four began in November 1761. Harrison, now sixty-eight years
old and not up to a voyage to the West Indies, entrusted the clock to his son and
co-craftsman, William. By arrangement with the Board of Longitude, the timekeeper was
placed aboard the Deptford, bound for Jamaica, and secured in a case with four locks.
The four keys were given to William Harrison, Governor Lyttleton of Jamaica, who was
taking passage on the ship, Captain Dudley Digges, and his lieutenant. All four had to
be present, with their keys to unlock the case at each winding.
Nine days out the Deptford's longitude, by dead-reckoning, was 13 50' W, but according to
Harrison's calculations, based on the timepiece, it was 15 19' W - a difference of nearly
160 kilometers. Harrison told a skeptical Captain Digges that if Madeira was properly
placed on the chart they should sight land the next day. Despite his reservations, Digges
held to Harrison's course. At 6 a.m. the next day, the lookout reported seeing land dead
ahead. It was Porto Santo, the northeaster island of the Madeira group.
The landfall of Jamaica was equally successful. The Deptford, following Harrison's
predictions throughout the voyage, arrived three days before another ship that had sailed
for Jamaica ten days earlier. Number Four was taken ashore and checked against
Jamaica's longitude, as determined by astronomical observations. After allowing for the
predetermined rate of error (2-2/3 seconds a day), the clock was found to only 5 seconds
slow. This meant an error in longitude of 1.25' - or 1.25 nautical miles, 2.3 kilometers.
Number Four had more than complied with the requirements for the great prize.
On the return voyage, Number Four was put through the shocks and stresses of extremely
stormy weather. Nevertheless, when it was checked back in England, its total error in
longitude for the five-month round-trip voyage was 28.5'. The timepiece was within the limit
of half a degree. But, if John Harrison had earned the prize, he had yet to win it.
Harrison, when he sought to collect the money, encountered stubborn resistance from
the Royal Society and the Board of Longitude, the very body that had encouraged him
during the long years of labor. The board decided that the clock's performance could have
been a fluke. Harrison was awarded L2,500 as an interim prize and was told that the full
prize would be his only if he submitted his clock to an examination of its mechanism and
to another and more exacting trial at sea.
He had little choice but to submit. His son William embarked this time in March 1764 aboard
the Tartar, bound for Barbados, with John Lindsay as captain. Once again, Harrison correctly
predicted the landfall at Madeira and also at Barbados. And who should be at Barbados
when Harrison arrived but Nevil Maskelyne, who had been sent out to compare Harrison's
results with observations of Jupiter's satellites. The board was taking no chances.
Number Four, however, had performed even better than on the voyage to Jamaica. The timepiece
showed an error of 38.4" over a period of seven weeks, or 15.36 kilometers of longitude. Further
calculations showed that, after the round trip, the error came to less than one tenth of a second
a day.
In resolution in early 1765, the Board of Longitude unanimously concluded that, "the said
timekeeper has kept its time with sufficient correctness, without losing its longitude in the
voyage from Portsmouth to Barbados beyond the nearest limit required by the Act 12th of
Queen Anne, but even considerably within the same." But it still withheld the full prize,
declining to pay more until Harrison had disclosed the secrets of his timepiece, so that it
could be reproduced, and had turned over all four machines to the board.
Harrison was an old man by this time, and his eyesight was failing him. "I cannot help thinking,"
he wrote to the board, "but I am extremely ill used by gentlemen who I might have expected
different treatment from... I hope I am the first, and for my country's sake, shall be the last that
suffers from pinning my faith on an English Act of Parliament."
George III had an informed and sympathetic interest in technology. He had been so impressed
by the accounts of the Tartar's voyage that he had granted Harrison and his son an audience at
Windsor. And so Harrison now asked for another audience in which to state his case, the case
for his Number Four. The audience was granted, and upon hearing the story, George III lost his
patience. "By God, Harrison, I'll see you righted," the king declared, and so he did.
Harrison's Number Five, which he had been ordered to build, was tested at the king's private
observatory at Kew. George II took a daily interest in checking the clock's performance. In ten
weeks the clock was in 4-1/2 seconds, and average of nearly 1/14 second per day. The kin
needed no further proof, and instructed Harrison to petition Parliament for the full prize.
Everyone in Parliament knew the petition had the backing of George III and that he was willing,
if necessary, to testify in Harrison's behalf. This did not prove to be necessary. In 1773 Harrison
received the balance of the L20,000 prize.
"Longitude Harrison," as he was often called, died at his house in Red Lion Square in London
on March 24, 1776, in the eighty-third year of his life. He had provided the instrument for bringing
a new dimension to navigation and mapping, the dimension of longitude. The instrument was the
earliest version of the modern marine chronometer.
In the year of Harrison's death, James Cook sailed again to the Pacific, where he demonstrated
beyond any doubt the utility of the chronometer in marine mapping. Nearly two centuries later,
the honored guest at a dinner at 10 Downing Street was an American, who rose to propose a toast
to John Harrison. His invention, the American said, enabled men to explore the Earth with
precision and, when most of the Earth had been explored, to dare to build navigation systems for
voyages to the Moon. "You, ladies and gentlemen, started us on our trip."
The speaker was Neil. A. Armstrong.
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