Benjamin Franklin Papers

# From ———5

(incomplete): American Philosophical Society

The accurate determination of longitude by a ship at sea long remained an unsolved problem.6 Several theoretically possible methods were advanced during the two centuries and a half after Columbus, but when put to actual test none proved both practicable and sufficiently reliable to serve the needs of mariners, especially of those embarked on long east-west voyages, such as the crossing of the ocean. So urgent did the matter become that several large prizes were offered for the discovery of an accurate and usable method. Among these the British Parliament offered in 1714 a prize of £20,000 for any method capable of determining a ship’s longitude within half a degree, with proportionately smaller prizes for methods of lesser exactitude; grants were also provided to assist promising experiments. The act placed the administration of the scheme in the hands of commissioners commonly called the Board of Longitude.7

The most promising method—and the one which ultimately won the prize—was by the construction of a timekeeper more reliable than any previously built, which, once set to accord with the local time at some point of known longitude, such as the Royal Observatory at Greenwich, England, could be carried on shipboard and compared with the local time at sea as found by celestial observation. The time when the sun or moon, for example, will be at a certain position in the sky at Greenwich on a given date can be predicted and set down in a table prepared in advance, and, since the earth revolves through one degree every four minutes, it becomes a simple calculation to convert the difference between Greenwich and local ship’s time into degrees, minutes, and seconds of longitude east or west of Greenwich.8 That is, it is a simple matter if the timekeeper is unaffected by the ship’s motion, even in a heavy storm, or by changes in temperature, humidity, gravity (at different points on the earth’s surface), or other external conditions. It may gain or lose somewhat if that gain or loss is constant and has been ascertained in advance, but it must not fluctuate erratically. To determine the longitude of a ship within half a degree, after six weeks at sea, the timekeeper must be accurate to approximately three seconds a day throughout the voyage. And an error of considerably less than half a degree in determining a ship’s position in unpropitious weather has often spelled disaster.9 At the time of the Act of 1714 no timekeeper made could come close to meeting these conditions when taken to sea.

Inevitably the huge rewards offered by Parliament attracted the attention not only of mathematicians and ingenious mechanics, as they were intended to do, but also of cranks and visionaries, some of whom were as sure that they had solved this problem as they were that they could square the circle or create perpetual motion. The unknown writer of this letter to Franklin may indeed have been something of an ingenious mechanic, as he clearly esteemed himself to be, but even if one discounts heavily his inability to express himself with entire clarity, it seems necessary to class him with the many enthusiasts who bombarded the Board of Longitude with unworkable schemes for solving not only the problem officially before it but others quite outside its province.

It is an interesting coincidence, however, that the man who ultimately did win the parliamentary £20,000 for his chronometer, John Harrison (1693–1776), was at this very time completing one of his preliminary models in England and planning the device, finished in 1759, which won him the first half of the grand prize.1 And there is perhaps a touch of irony in the fact that Harrison, the son of a Yorkshire carpenter with virtually no formal education, could not put his ideas on paper any more effectively than could Franklin’s Philadelphia correspondent. There is no evidence that Franklin ever brought this letter to the attention of the Board of Longitude after he reached England. He did, however, pay Harrison 10s. 6d. on Dec. 1, 1757, “to see his Longitude Clock.”2

Worthey Sir

This I first made goe with two Globs and two Triangles but Now Goes With a Single of Each for the more Convenencey of Putting it into Watch Work.

Now Gentlemen I have Given you a Draught of it Exacttley How I Draw it on Steel and Brass and file and turn it Putt it to Geather and it shall ware time out of mind for Letts Reason a Common Watch has two Braking Pins Which Causess it to Hurrey and Go So much faster at Some times and So Slow at others. The Horizontial ones has remedyd this Misfortune but has one as Great that is if they are un[illegible] in Winding She Will Stop a Little8 [Dirtey?] is the Same and the Worst Take of[f] the Regulating Spring or you Cannot move the Celinder. If you Press the Wheel so as to Break it and the Nex thing It is not till further [sic] for I shall Describe my owne but this I can assure you this of mine is Such that it moves So Light that your 1 or 2 Pinion Shall be wore out Sooner than the Regulating Cause that is the Triangles and Globes besides the force Given is Such that Without the Regulating Spring you Cannot Stop them. No Longer than you hold your finger or Point against the Moveing Cause though I make it Go true time without a regulating Spring I mus Needs Say that if you Saw one you would Say as Samuel Kirk said the most ignorant man in the World Would be Convins’d its So Demonstriable to Sight that I Cannot Describe it With my Pen. You Can No more Err in Makin the Size of Each triangle and Globe than in Makeing a Pinion of 6 to a Wheel of 48 for to Make it Ware well it must be the Height of [illegible] and an [?] but How to Regulate this. [Remainder missing].

[Note numbering follows the Franklin Papers source.]

5The author of this letter has not been identified. He was obviously a Philadelphia clock- and watchmaker who was not personally acquainted with . The wording of his letter suggests that he was a man of limited education, or, at least, that a writer’s pen was not one of the tools he could use most successfully. In the list of clockmakers of Philadelphia given in George H. Eckhardt, Pennsylvania Clocks and Clockmakers (N.Y., 1955), pp. 168–99, the following appear to be possibilities: Johann Ent, Augustine Neisser, Thomas Stretch, and Christopher Witt.

6Much of this headnote is based upon Rupert T. Gould, The Marine Chronometer Its History and Development (London, 1923), esp. pp. 1–70.

7An Act for providing a Publick Reward for such Person or Persons as shall discover the Longitude at Sea, 12 Anne c. 15.

8For example, if the timekeeper shows Greenwich time to be 1:00 P.M. at the moment when observation from the ship shows local time to be exactly noon, the ship is precisely fifteen degrees west longitude from Greenwich.

9Relationship between degrees of longitude and nautical miles varies with the latitude. A nautical mile (1.1516 statute miles) equals one degree of longitude at the equator. Half a degree at the 40th parallel, the latitude of Philadelphia, is roughly 23 nautical miles.

1Harrison’s earlier timekeepers won him the Copley Medal of the Royal Society in 1749. His timekeeper No. 3 was finished in 1757 and he began at once to construct No. 4, which Gould calls “the most famous chronometer that ever has been or ever will be made” (Marine Chronometer, p. 49). It was placed on a naval vessel in 1761, carried on a voyage to Jamaica, tested there, returned to England on another ship, and proved to have a total unpredicted error during five months and two ocean crossings of only 1 minute, 53½ seconds of time or 28½ minutes of longitude. A second trial in 1764 showed even less error and the Board of Longitude reluctantly (because its members suspected a fluke) agreed to award Harrison £10,000. A protracted dispute followed but finally, through the intervention of King George III, a special act of Parliament appropriated to him the second half of the grand prize in 1772. Including grants to assist his experiments, Harrison received a total of £22,550 from the Government for his work. Ibid., pp. 40–70.

2“Account of Expences,” p. 8; PMHB, LV (1931), 106.

3It would appear from this and later passages that the writer thought it was the Royal Society, rather than the Board of Longitude, which was to make awards for discovering a method of determining longitude.

4Possibly Lewis Evans is intended here, though the editors have found no evidence to show that he was the sort of man who would be guilty of the duplicity here charged.

5Probably Edward Duffield (1720–1801) clock- and watchmaker of Philadelphia, 1741–47, and later of Lower Dublin, Philadelphia Co. He made at least one clock for , was elected to the , and was one of the executors of ’s last will.

6John Tinker (d. 1758), governor of the Bahamas from 1740 to his death, visited Philadelphia in the fall of 1754 and attended the Academy exercises on November 12. Pa. Gaz., Nov. 14, 1754.

7Evidently the writer, like numerous others, believed erroneously that the Act of 1714 provided rewards for discovering perpetual motion as well as a method of determining longitude.

8While the writer’s exact meaning cannot be determined, this is clearly a reference to a common failing of early clocks and watches, which stopped when the motive power (whether a spring or a weight) was being rewound. The difficulty had been overcome by Jeremy Thacker in 1714 and again independently by John Harrison in 1735 by the addition of an auxiliary spring called the “maintaining power.” Gould, Marine Chronometer, pp. 34, 44.