The Principles of Mr. Harrison's Time-Keeper, with Plates of the Same. Published by Order of the Commissioners of Longitude

Ten folding engraved plates. 31 pp. Large 4to, cont. half-calf & marbled boards, spine gilt, red morocco lettering piece on spine. London: Printed by W. Richardson & S. Clark; and sold by J. Nourse & Mess. Mount & Page, 1767.

[bound with]:

MASKELYNE, Nevil. An Account of the Going of Mr. John Harrison's Watch, at the Royal Observatory, from May 6th, 1766 to March 4th, 1767. Together with the Original Observations and Calculations of the Same...Published by Order of the Commissioners of Longitude. 28, lvi pp. Large 4to. London: W. Richardson & S. Clark, 1767.

[bound with]:

LE ROY, J[ulien] D[avid]. A Succinct Account of the Attempts of Mess. Harrison and Le Roy, for finding the Longitude at Sea, and of the Proofs made of their works...To which is prefixed, a Summary of the Marquis de Courtanvaut's Voyage, for the Trial of certain Instruments for finding the Longitude at Sea. Done from the French, by a Fellow of the Royal Society. 14, xii, 54pp. Large 4to. London: F. Newbery, 1768.

First editions of the first two works and first edition in English of the third; very fine copies from the library of Matthew Boulton, with the modern bookplate. These are important works regarding the invention and perfection of the chronometer, which enabled navigators to determine their correct geographical position at all times.

I. While latitude has been ascertainable by relatively simple means, measuring longitude presented considerable challenges. In 1714, the English government offered the enormous prize of 20,000 pounds to be awarded by the Board of Longitude to anyone who developed a reliable means of calculating longitude at sea. "One way of measuring longitude is to compare local solar time with the standard time at the prime meridian. Local time is easily ascertained by observing the sun but only a very accurate clock can register a standard time over long periods. The improvements in horology effected by Christian Huygens and others after him about the mid-seventeenth century promised success with this method. But the practical problems associated with temperature-compensation and so forth remained long intractable, although several rewards for an invention were offered. Finally, John Harrison, a clockmaker with several useful inventions to his credit...perfected a chronometer of the required degree of accuracy, showing a steady rate of gain or loss. Harrison's chronometer not only supplied navigators with a perfect instrument for observing the true geographical position at any moment during their voyage, but also laid the foundation for the compilation of exact charts of the deep seas and the coastal waters of the world...There has possibly been no advance of comparable importance in aids to navigation until the introduction of radar."-Printing & the Mind of Man 208-(describing Harrison's earlier An Account of the Proceedings: 1763).

II. As part of the dispute between Harrison and the Board of Longitude, Maskelyne was called upon to test the accuracy of Harrison's marine chronometer. Maskelyne was known to favor the rival method of finding longitude by means of lunar tables and he therefore subjected Harrison's chronometer, which had already performed well on two West Indian voyages, to a series of extreme and unrealistic tests. The tests were intended to fully discredit the watch. The predictably disappointing results were published in the present pamphlet, along with Maskelyne's conclusion that "Mr Harrison's watch cannot be depended upon to keep the longitude within a degree in a West India voyage of six weeks...nevertheless...it is a useful and valuable invention."

III. First edition in English of the Exposé succint des Travaux de MM. Harrison et Le Roy (1768). This is a very rare and important contribution to the famous and bitter quarrel involving Pierre Le Roy (1717-85), the most eminent horologist in France of the 18th century, Harrison, and Berthoud. Le Roy made important contributions to the chronometer; he "established the main principles of the modern chronometer, to wit, a detached escapement, temperature compensation in the balance, and an isochronous balance spring."-Catherine Cardinal, "Ferdinand Berthoud and Pierre Le Roy..." in The Quest for Longitude (Ed. by William J.H. Andrewes), 1996, p. 292. The present work was written by Le Roy, using his father's name for this edition, in answer to Harrison's Principles (see item I). Le Roy illustrates the originality and priority of his own work, dating from before 1754, in comparison with Harrison's. While recognizing the merit of Harrison's chronometer, he considered his own to be superior. The condescension expressed here by Le Roy provoked a series of violently critical responses, both in England and in France.

Le Roy also provides an account of the trial of his Nos. 1 and 2 on the Aurore under the Marquis de Courtanvaux in 1767.

This is an extremely rare book.

Fine copies, attractively bound together, and preserved in a box. Loosely inserted is a page of manuscript notes in ink by a contemporary reader about Harrison's time-keeper.

❧ I. Horblit 42b. II. Baillie, Clocks and Watches. An Historical Bibliography, p. 271. III. Baillie, ibid., pp. 276-77-(describing the original French edition). See also the note to Printing & the Mind of Man 208 for a discussion of the claims of Le Roy to priority in the invention of the chronometer.