Page:Dictionary of National Biography volume 15.djvu/202

 (Mem. R. A. Soc. xxxv. 144;, Encycl. Brit. xvi. 252). Dollond also independently invented in 1819, and was the first to construct, a micrometer similar to the ‘dioptric’ one described by Ramsden in 1779, in which the principle of the divided lens was adapted to the eye-piece. Dr. Pearson procured one from him for twelve guineas, but found it too heavy for use with an ordinary achromatic (, Practical Astronomy, ii. 184).

On 13 April 1821 Dollond communicated to the Astronomical Society a ‘Description of a Repeating Instrument upon a new construction’ (Mem. R. A. Soc. i. 55), a kind of altazimuth in which the repeating principle was applied to both vertical and horizontal circles; and on 14 Nov. 1823, ‘A Short Account of a new Instrument for Measuring Vertical and Horizontal Angles’ (ib. ii. 125), otherwise called a ‘double altitude instrument,’ with which altitudes could be taken by direct and reflected vision simultaneously, thus dispensing with level or plumb line. His ‘Account of a Concave Achromatic Glass Lens as adapted to the Wired Micrometer when applied to a Telescope, which has the Power of increasing the Magnifying Power of the Telescope without increasing the Diameter of the Micrometer Wires,’ was read before the Royal Society on 27 Feb. 1834 (Phil. Trans. cxxiv. 199). It described a skilful application of Barlow's concave lens to the micrometer, specially designed to meet Dawes's needs in double-star measurement, and highly approved by him. Dollond's last invention was an ‘atmospheric recorder,’ for which he received the council medal of the Great Exhibition of 1851. By its means, varying atmospheric pressure, temperature, force and direction of wind, rainfall, evaporation, and electrical phenomena registered themselves simultaneously during periods limited only by the length of paper on the roller.

Dollond took an active part in the foundation of the Astronomical Society in 1820, and attended diligently at the council meetings until near the close of his life. He was elected a member of the Royal Society on 23 Dec. 1819, and was one of the original fellows of the Royal Geographical Society. He observed the partial solar eclipse of 7 Sept. 1820 at Greenwich (Mem. R. A. Soc. i. 138). In his business relations he set an example of probity and punctuality; he was highly esteemed in private life, and enjoyed the friendship of the leading scientific men of his time.

[Monthly Notices, xiii. 110; Journ. Geog. Soc. 1853, p. lxxiii; R. Soc. Cat. of Scientific Papers; a Catalogue of the Instruments sold by Dollond in 1829 is contained in Astr. Nach. viii. 42.]  DOLLOND, JOHN (1706–1761), optician, was born at Spitalfields on 10 June 1706, of Huguenot parents, who had fled from Normandy to London on the revocation of the edict of Nantes. The conjectured original spelling of their name as d'Hollande implies that they were of Dutch extraction. Dollond was brought up to the hereditary trade of silk-weaving, and his father's death, while he was still a child, compelled the sacrifice of his education to the necessities of his family. But no impediments could debar him from self-improvement. His studies embraced Latin, Greek, anatomy, theology, no less than algebra and geometry; and his recreation at the age of fifteen consisted in solving problems, drawing figures, constructing sundials, &c. An early marriage restricted his little leisure; yet he contrived, by curtailing sleep, to attain proficiency in optics and astronomy, the subjects of his later and lasting devotion.

In 1752, his eldest son, Peter Dollond [q. v.], having set up as an optician, he abandoned silk-weaving to join him, and rapidly attained the practical skill for which his theoretical acquirements had laid the foundation. His first appearance before the learned world was in a controversy on the subject of Newton's law of refraction with Euler, who in the ‘Berlin Memoirs’ for 1747 (p. 274) had endeavoured to substitute for it a hypothetical principle permitting the colour-correction of telescopes by the employment of combined lenses of glass and water. Dollond expressed his objections in a letter to James Short [q. v.] dated 11 March 1752, which Short persuaded him to send to Euler, and communicate, with his reply, to the Royal Society. It appeared in the ‘Philosophical Transactions’ with the title ‘A Letter concerning a Mistake in M. Euler's Theorem for correcting the Aberrations in the Object-Glasses of Refracting Telescopes’ (xlviii. 289). Because Newton, on the strength of his celebrated ‘eighth experiment’ (described in his ‘Opticks,’ 3rd edit. p. 112), had despaired of correcting colour-aberration by a multiplicity of refractions, Dollond declared it to be ‘somewhat strange that anybody nowadays should attempt to do that which so long ago has been demonstrated impossible.’ A geometrical investigation by Klingenstierna, a Swedish mathematician, nevertheless showed the inconsistency with known optical phenomena of Newton's law of dispersion, the truth of which was assumed by Dollond. Upon hearing of this in 1755 he, however, decided to repeat the fundamental experiment upon which the contested