(24 Mar 1693 - 24 Mar 1776)
John Harrison and the Longitude Watch
from Stories of Inventors and Discoverers in Science (1860)
by John Timbs
[p.116] The method of ascertaining Longitude by means of the Watch is briefly as follows. If a navigator has a chronometer showing him the exact time at Greenwich, the instant that the sun comes to his meridian it is twelve o’clock, and the difference between this time and the hour marked by the chronometer gives him his Longitude; or, when the time is known at which any particular star passes the meridian at Greenwich, if the navigator marks the instant at which the star comes to his meridian, the difference between this time and the time it would appear at Greenwich is the difference in Longitude.
This problem had, however, been but inaccurately solved for want of good watches. Huyghens is supposed to have been the first who thought of constructing timekeepers for this purpose; but at that period, 1664, sufficient attention had not been paid to the effects produced on metals by the variations of temperature in different climates, and he unfortunately failed in his experiments. Maritime nations had already promised rewards to any one who should make the discovery. In 1598 Philip III. of Spain offered a prize of 1000 crowns; the Dutch followed this example; the Duke of Orleans, Regent of France, offered in the name of the king 100,000 livres; and the French Academy awarded annually a prize to those who made the most useful discoveries connected with the subject. The English, being the greatest navigators, were most interested; and in 1714, Parliament appointed a committee to consider the question, foremost of whom was Sir Isaac Newton, who at once suggested the discovery of the Longitude by the dial of an accurate timekeeper; and upon their recommendation the legislature of Queen Anne, in 1714, passed an act granting 10,000l. if the method found discovered the longitude to a degree, or 60 geographical miles; 15,000l. if to 40 miles, and 20,000l. if to 30 miles; to be determined by a voyage from a port in Great Britain to any port in America. At length, after the golden promises of sovereigns, and the researches of the greatest philosophers of the age, had for nearly a century and a half failed in the great discovery, it was made by a self-taught genius, [p.117] who was bred a village carpenter, and never acquired any acquaintance with literature.
John Harrison was born at Faulby, near Pontefract, in Yorkshire, in 1693; he was the son of a carpenter, which occupation he followed for several years: yet he very early manifested a taste for mathematical science, said to have been first awakened by a copy of some lectures of Saunderson the blind mathematician, that accidentally fell into his hands. He was also fond of mechanical pursuits; and before he was twenty-one he had made two wooden clocks by himself, and without having received any instruction in the art. His residence in view of the sea is said to have led him to devote himself to the construction of marine timepieces, and in 1728 he first came up to London to prosecute this object; in 1736 he completed the first chronometer used at sea—it neither varied from change of temperature nor the motion of the vessel. Having obtained certificates of its excellence from Halley, Graham, and others, this timekeeper was placed on board a ship of war going to Lisbon, the captain of which attested that Harrison had corrected an error of about a degree and a half upon their return to the English Channel. The Parliamentary Commissioners now presented Harrison with 500l., to enable him to proceed with his experiments. In 1739 he produced a smaller chronometer, which promised to give the longitude with even greater accuracy. In 1741 he finished another smaller than either, which the Fellows of the Royal Society considered to be more simple, and less likely to be deranged; and in 1749 Harrison received the Society’s gold medal.
Having much improved and corrected this third chronometer, Harrison claimed a trial of it; and the commissioners accordingly, in 1761, sent out his son William in a king’s ship to Jamaica. After eighteen days' navigation, the vessel was supposed to be 13° 50' west of Portsmouth, while the watch, marking 15° 19', was condemned as useless. Harrison, however, maintained, that if Portland Island were correctly marked on the chart, it would be seen on the following day; in this he persisted so strongly, that the captain was induced to continue in the same course, and accordingly the island was discovered the next day. This raised Harrison and his watch in the estimation of the crew, who otherwise would not have been able to procure the necessary stores during the remainder of the voyage. In like manner, Harrison was enabled by his watch to announce all the islands in the order in which they would fall in with them. On his arrival at Port Royal, after a voyage of eighty-one days, the chronometer was found to be about five seconds slow; and on his return to Portsmouth, after a voyage of five months, it had kept time within about one minute five [p.118] seconds, which gives an error of about eighteen miles. This was much within the limits of thirty miles prescribed by the Act of 1714, and Harrison claimed the reward; but several objections being taken to the proofs, William Harrison made a second voyage, which left no further doubt of Harrison’s claim, his chronometer having determined the position of Barbadoes within the limits prescribed by the Act. The sum of 20,000l. was then awarded to him—10,000l. immediately on his explaining the principle of construction, the other half on its being ascertained that the chronometer could be made by others. Liberal as this reward appears, it must be remembered that Harrison devoted upwards of forty years before his inventions were perfected, or their general merit fully established. The most important of these improvements are the gridiron pendulum and the expansion balance-wheel; the one serving to equalise the movements of a clock, and the other those of a watch, under all changes of temperature; and both depending upon the unequal stretching, under change of temperature, of two different metals, which are so employed to form the rod of the pendulum and the circumference of the wheel, that the contraction of the one exactly counterbalances the expansion of the other.1 Another of Harrison’s important inventions is the going fusee, by which a watch can be wound up without interrupting its movement. This curious machine, as well as the other timekeepers of Harrison, is still preserved at the Royal Observatory, Greenwich. Being discovered there in a very dilapidated state several years ago, it was put in repair at the expense of Messrs. Arnold and Dent. Excepting the escapement-wheel, all the wheels were of wood,—merely flat discs with wooden teeth. The pinions also were of wood. Mr. Dent states that the arrangements for obviating friction were so admirable, that on the removal of part of the escapement the train of wheels ran down with great velocity, although they had not revolved for more than a century before.
Harrison died at his house in Red Lion-square in 1776, in his eighty-third year. On mechanics, and subjects connected with that science, he could converse clearly; but he found great difficulty in expressing his sentiments in writing, as is evident from a work which he left on the construction of timepieces. Still his labours present a remarkable instance of what natural genius can accomplish in one particular line without cultivation.
It should, however, be added, that the complexity of [p.119] Harrison’s timekeeper, and its high price, 400l., left to be invented, for practical purposes, an instrument of greater simplicity, in the timekeeper of John Arnold, for which he and his son received the Government reward of 3000l.3 In this machine each part performs unchecked the office assigned to it; and its extreme variation in twelve months has been 57-hundredths only. It is therefore highly honourable to the English artists, that by their ingenuity and skill they have accomplished the great object which had occupied the attention of the learned of Europe for nearly 300 years, namely, the means of discovering the Longitude at Sea.
In 1793 a committee of the House of Commons gave to Thomas Mudge, a London watchmaker (or to his son for him), in opposition to the opinion of the Board of Longitude, a reward of 3000l. for inventing a remontoire escapement for chronometers, “not worth a farthing,” says Mr. E. B. Lenison, “and, as indeed it turned out, worth a great deal less to his son, who proceeded to make the chronometer.” Mr. Denison maintains that Thomas Earnshaw brought the chronometer to the state in which it has remained for the last eighty years, with scarcely any alteration: the chronometers of inferior artists were always beaten by his, whenever they came into competition; and these artists afterwards copied Earnshaw’s inventions, and did their best to prevent his being rewarded for them.
The English chronometers, on the whole, enjoy a reputation superior to those of any other nation; nevertheless the latter have attained high excellence. One of the New-York chronometers supplied to the Grinnell Arctic Expedition was subjected to all sorts of exposure to which such instruments are liable in a Polar winter; but was so exquisitely provided with adjustments and compensations for the very great extremes of temperature to which it had been subjected, that it was returned with a change in its daily rate, during a year and a half, of only the eighteen-thousandth part of one second of time. It should be borne in mind, that the temperature registered during the winter in Wellington Straits was actually 46” below zero. 3
2 Arnold is celebrated for the manufacture of the smallest repeating watch ever known: it was made for George III., to whom it was presented on his birthday, June 4, 1764. Although less than six-tenths of an inch in diameter, itrepeated the hours, quarters, and half-quarters, and contained the first ruby cylinder ever made. It is the size of a silver twopenny-piece, and its weight that of a sixpence. So novel was its construction, that Arnold not only designed and executed the work himself, but had to manufacture the greater part of the tools employed in its construction. The King presented 500 guineas to Mr. Arnold for this curious watch: and the Emperor of Russia afterwards offered the maker 1000 guineas for a duplicate of it, which he declined.
3 Alderman Carter, elected Lord Mayor of London in 1859, is a very successful chronometer-maker, having received several Government rewards.