British clockmaker who solved the problem of determining Longitude at sea. Harrison's contribution was the development, between 1730 and 1760, of a robust and portable series of clocks suitable for sea voyages. By comparing a highly accurate portable clock set to the time at the home port, with the ship local time (say, at noon), it became possible to compute the degrees east or west of the meridian of the home port.

Since the globe has 360 degrees longitude and there are 24 hours, every hour difference between the clocks corresponds to 15 degrees longitude.

A most amazing man and a freaking genius.

By all accounts John Harrison (born 1693) was a self taught watchmaker who invented seaworthy clocks for the purpose of solving the problem of longitude. As a teenager, in a country township, a local clergyman encouraged Harrison's curiosity of the way things worked by letting him borrow a manuscript copy of a lecture series on natural philosophy delivered by mathematician Nicholas Saunderson at Cambridge University. Harrison, who already knew how to read and write, made his own annotated copy - writing out every word and labeling every diagram. He continued to add notes and observations to his copy of the manuscript for years to come.

His earliest clocks were made from wood and exhibited his outstanding carpentry skills (learnt from his father) and ingenious insights into solving the problems of timekeeping in the early 1700s. As he gained a reputation for making clocks, his first major work was commissioned - a tower clock on the stable of a local manor house, included these features:

  • The selection of woods. Oak wheels and boxwood axles. Harrison selected fast growth oak wood trees for the wheels. Faster growing trees have timber with a wider grain and greater strength making them more suited for use in clock wheels. In the axles, where less strength was required, he used slower growing timber that weighed less.
  • The working of wood. Harrison worked the wood so that the wood grain radiated from the centre of the wheel to the tips of the teeth. This, along with the selection of timber, ensured the clock would work for many years to come without need of repair.
  • Friction free gearing. Harrison designed a clock that didn't need any oiling. The use of oil at the time was problematic as thery were often made out of concoctions of plant (nut oils or olive oils) and animal fats (whale). These oils would often foul up the workings of a clock. In order to avoid using any of these oils, and to reduce maintenance, Harrison carved some parts out of lignum vitae - a tropical hardwood that exudes its own grease.
  • The use of brass. Wherever it was needed Harrison used brass instead of steel so that corrosion could be avoided.

These were the first stepping stones to further advances by John Harrison towards the goal of creating seaworthy clocks. He later worked on building grandfather clocks that showed increases in precisions due the incorporation of the following features:

  • The Gridiron. Two different metals (brass and steel) placed alternately to form the shaft of the pendulum countered the effects of changes in temprature. Heat and cold increases and decreases the length of a single metal pendulum causing the clock to become inaccurate.
  • The Grasshopper. An escapement (the thing that makes the tick tock sounds) that was without friction ( and

Harrison's grandfather clocks, built from 1725-1727 with the help of his brother James, were reasonably accurate. At the time, timepieces were quite inaccurate and even the highest precisions clocks manufactured by respected watchmakers in most cases lost a minute per day. Harrison's clock lost only a single second in a whole month. Precision was important in the quest to solve the problem of longitude where ships would often travel for weeks or even months, so accuracy was paramount. But a seaworthy clock had to remain accurate even as the shipped moved with the ocean and be reliable under conditions of extreme heat and cold and in the presences of salt water. Having solved the latter issues, Harrison then worked on replacing the pendulum system with something much more advanced that would work as the ship moved. He began to design a solution specifically for the board of longitude.

In 1735, after five years of work, Harrison built the H-1 (Harrison No. 1), with the financial help of "Honest" John Graham ( a watchmaker friend of Dr. Edmond Halley), that incorporated a link balanced mechanism which worked with precision regardless of any change in motion or direction in gravity. H-1 was made totally out of brass and would run for one day without rewinding. It weighed in at 75 lbs and was 4 feet high, wide and deep. Tests on a ship to Lisbon proved that it kept time accurately but Harrison who was a perfectionist requested more money from the board to develop H-2. Note: The different sources I have read give conflicting information about the ability of Harrison's clocks to meet the requirements of the board of longitude. Some say H-2 (and H-3 for that matter) was accurate enough, some say it was not. Sobel's, in his book makes a qoiute saying thaH-2 was accurate enough to meet the limits, and then some of the board of longitude.

H-2, which was smaller than H-1, but weighed 80 lbs, was finished in 1737. It included even more amazing features. Even that it had a more responsive temperature compensation device and a uniform drive mechanism Harrison still was unhappy with some deficiencies he saw in it. Even though there was critical acclaim for the clock from the Royal Society, Harrison was keen to create H-3 to right the wrongs of previous versions. Harrison then spent 20 years creating a circular balance mechanism.

H-3, included 735 parts, weighed 60 lbs, was 2 feet high and 1 foot wide, and contained:

  • a bi-metallic strip which compensates automatically for changes in temperature. This same mechanism is used in thermostats today.
  • caged ball bearings to reduce friction. These are also used today in almost all machinery.

However during this time Harrison, who had been living in London, met many watchmakers and a friend, John Jeffreys, built a small pocket watch fitted with a bi-metallic strip that could also remaing working while being wound. Here again recounting of history differs. Some say Harrison commissioned the watch, others say Jeffreys built the watch based on Harrison's design. Regardless, it was Harrisons design in "miniature" - it weighed 3 lbs and was 5 inches in diameter, and kept time amazingly well. This was at a time when pocket watches were not considered to be serious time keepers. After two months at sea, H-4 was found to be only 5.1 seconds slow. H-4 incorporated diamond and ruby gear teeth to reduce friction. It is still not known exactly how or why Harrison came upon this approach or what technique he used to shape them. Finally Harrison was satisfied:

I think I may make bold to say, that there is neither any other Mechanical or Mathematical thing in the World that is more beautiful or curious in texture than this my watch or Timekeeper for the Longitude... and I heartily thank Almighty God that I have lived so long, as in some measure to complete it." (pp 106. Sobel)

Despite this great achievement the board of longitude tested the clock for 12 years and Harrison was 80 before he received his prize (3 years before he died). Many competing approaches were presented to the board of longitude and Harrison's watches were closely scrutinised and were also shunned as some form of accidental freak or were merely accurate through luck or chance. Harrison was required to build two identical clocks for testing. The board also wanted to know how it worked and wanted possession of the watches. This caused a great deal of tension. At 79 years of age. harrison made an appeal to King George III, who upon summoning Harrison stated that he had been wronged and "...By God Harrison, I will see you righted!" Even though the King tested H5 (the copy of H4), and found it worked perfectly, the board of longitude did not award Harrison the prize money, which had to be won through an act of parliament in June 1773.

Sobel, D. (1998). Longitude. Fourth Estate: London.

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