DGLLOND, JOHN, .an eminent optician, was descended from a French refugee family, settled in Spitalfields, end born on the 10th of June 1706. His parents were in humble circumstances, his father being an operative silk weaver; and the son was brought up to the same occupation. Tho little leisure however which ho had was spent in the acquisition of a varied circle of knowledge. Besides the study of mathematics and physic., to the latter of which his reputation is chiefly due, ha studied anatomy and natural history in general, on the one hand, and theology and ecclesiastical history on the other. In furtherance of this diversified class of subjects, which, considering the toil to which the day was devoted, was sufficiently extensive, he undertook the Greek and Roman chalice ; he was partially acquainted with several Of the modern languages, bet with French, German, and Italian he was intimately conversant. Notwithstanding the cares of a family and the duties whleh it imposed upon him, Dollond still found means to cultivate the sciences ; and having apprenticed his eldest son, Peter, to an optical instrumenSmaker, he was in duo time able to establish him In business In Vine-court, Spitalfields. In this business he finally joined his son, for the cepeelal purpose, it would seem, of being able to unite his tastes with his business more perfectly than allk-weaving enabled him to do.
Immediately on We arrangement being completed, Dollond corn rnenced a series of experiments on the dispersion of light, and other subjects connected with the improvement of optical instruments, and especially of telescopes snd microscopes, the results of which were communicated to the Royal Society in a series of papers. Three of them were printed in the 'Philosophical Transactions' for 1753, one in 1754, and the last in 1758, the titles of which are given below. It wss about 1755 that he entered upon a systematic course of experi ments on dispersion, and after, to use his own words, a resolute perseverance' for more than a year and a half, he made the decisive experiment which showed the error of Newton's conclusions on this subject. The memoir in which the series of investigations was detailed appeared in the 'Philosophical Transactions,' and was the last which he gave to the world. It was rewarded by the council of the Royal Society with the Copley medal.
It was the lot of Dollond to undergo considerable annoyance on account of the claims set up for this discovery in favour of others, especially of Euler; but there is not a shadow of a doubt of Dol lond's priority as well as originality, in this very important discovery, left on the minds of the scientific world. The discrepancies which
followed the application of Newton's doctrine to the varied eases that presented themselves in the course of different experiments might, in epecu .tive minds, have created a suspicion of the accuracy of that doctrine; yet there does not appear to have been the least hesitation among acieutific men in attributing these discrepancies to errors of observation exclusively, and consequently not the least ground for honestly attempting to deprive Dollond of the honour of the discovery.
In the beginning of the year 1761 Dollond was elected a Fellow of the Royal Society, and appointed optician to the king. He did not long survive to enjoy the honour or advantages of his discoveries ; as on the 30th of September of that year, he was attacked by a fit of apoplexy, brought on by a too close and long continued application to o paper which he was studying. This attack immediately deprived him of speech, and in a few hours of life itself.
Besides his eldest son Peter, already mentioned (who survived him till 1820, when he died agei ninety), be left another son John, and three daughters. The two sous carried on the business jointly with great reputation and success; and upon the death of the younger in 1804, Peter Dollond took into partnership a nephew, George Huggins, who assumed the name of Dollond, and who continued the busi ness without diminution of the high character attached to the name of Dollond, till his death in May 1832. Mr. George Dollond trans mitted the now famous business to a nephew of his, also named George Huggins, and he in his turn obtained the royal permission to assume the surname of Dollond instead of Huggins.
The following is the list of John Dollond's published papers :-1, 'A Letter to Mr. James Short, F.R.S., concerning an Improvement in Reflecting Telescopes;' Phil. Trans.,' 1753, p. 103. 2, Letter to James Shdrt, A.M., F.R.S., concerning a mistake in Mr. Euler'a Theo rem for correcting the Aberration in the Object Glasses of Refractiog Telescopes; "Phil. Trans.,' 1753, p. 287. 3, 'A Description of a Contrivance for measuring Small Angles; "Phil. Trans.,' 1753, p.178. 4, An Explanation of an Instrument for measuring Small Augles ; ' Phil. Tram.; 1751, p. 551. 5, An account of some Experiments concerning the different Refrangibility of Light; "Phil. Trans.,' 1753, p. 733.