Dollond, John

(b. London, England, 10 June 1706; d. London, 30 November 1761)

optics.

Dollond was born in Spitalfields, London, of French Protestant parents who had originally lived in Normandy. Although he became a silk weaver, his inclination led him to the study of mathematics, astronomy, and the classical languages in whatever spare time he could find. His eldest son, Peter, joined him as a weaver but, stimulated by the knowledge of mathematics and optics learned from his father, subsequently took up the trade of optical instrument maker. This venture was successful, and John Dollond was consequently persuaded to leave the weaving trade. He joined Peter in business in 1752, and the partnership soon became fruitful.

Some ideas for the improvement of the optical arrangement of lenses in the refracting telescope were incorporated in a letter addressed to James Short, a fellow of the Royal Society, who communicated the letter to the society, where it was read on 1 March 1753. Soon after this, on 10 May 1753, another paper was read to the Royal Society, this time on an improved micrometer (heliometer) for the telescope. Dollond had modified the Savery micrometer by using one object glass cut into two equal segments instead of two whole lenses. The micrometer could now be applied to the reflecting telescope, which was immediately done by James Short.

Dollond is popularly known as the inventor of the achromatic telescope; but although he was anticipated in the discovery by about twenty years, it seems that he independently worked out the necessary lens combinations—and he certainly was the first to publish the invention and develop it commercially. Dollond’s early successes in optics brought him to the attention of astronomers and mathematicians. He corresponded with many, including Euler, against whom he defended Newton’s opinion that no combination of lenses could produce an image free of color, and that in this respect no improvement could be expected in the refracting telescope.

Eventually Dollond conducted (1757–1758) a series of experiments with different kinds of glass to check Newton’s findings. The paper incorporating the results, with the conclusion that the objectives of refracting telescopes could be made “without the images formed by them being affected by the different refrangibility of the rays of light,” was read to the Royal Society in June 1758. Dollond’s composite objective was patented, but the patent was challenged by a group of London optical instrument makers after his death. In 1766 the court upheld Peter Dollond’s right to the patent on the grounds that Chester More Hall, the inventor of an achromatic lens combination in the period 1729–1733, did not exploit the invention commercially or publicize his findings.

It seems unlikely that Hall’s invention could have been known to anyone capable of realizing its significance, because the Royal Society not only published Dollond’s papers but conferred both the Copley Medal (1758) and membership (1761) upon him. The certificate proposing Dollond for membership was signed in February 1761 by ten men, including scientists of the standing of Gowin Knight, John Smeaton, James Short, William Watson, and John Ellicott. The proposal specifically refers to Dollond’s invention of “an Object-Glass, consisting of two Spherical Lenses of different densities, so contrived as to correct the Errors arising from the different refrangibility of the Rays of Light.”

Early in 1761 Dollond was appointed optician to King George III. Regrettably, he did not enjoy this honor for long; he died of apoplexy later that year. He left three daughters and two sons, Peter and John. The latter joined his elder brother as a partner in the family firm.

BIBLIOGRAPHY

I. Original Works. The following were first published in Philosophical Transactions of the Royal Society and were reprinted in Kelly’s Life (see below): “A letter from Mr. John Dollond to Mr. James Short, F.R.S. concerning an Improvement of refracting Telescopes,” 48 , pt. 1 (1753), 103–107; “A Description of a Contrivance for measuring small Angles,” ibid., 178–181; “Letters relating to a Theorem of Mr. Euler, of the Royal Academy of Sciences at Berlin, and F.R.S. for correcting the Aberrations in the Object-Glasses of refracting Telescopes,” ibid., 287–296; “An Explanation of an Instrument for measuring Small Angles,” 48 , pt. 2 (1754), 551–564; and “An Account of some Experiments concerning the different Refrangibility of Light,” 50 , pt. 2 (1758), 733–743.

II. Secondary Literature. Reprinted letters and papers by John and Peter Dollond, Short, Euler, and Maskelyne will be found in John Kelly, The Life of John Dollond, F.R.S. Inventor of the Achromatic Telescope. With a copious Appendix of all the Papers referred to, 3rd ed. (London, 1808). For an account of the priority of Chester More Hall and the patent litigation, with references, see Thomas H. Court and Moritz von Rohr, “A History of the Development of the Telescope from about 1675 to 1830 based on Documents in the Court Collection,” in Transactions of the Optical Society, 30 (1928–1929), 207–260 (sec. IV, 228–235).

G. L’E. Turner