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 dent to a firm of coffee importers. But the firm failed, when Ross's foreman fortunately met him and begged him to return to his master's workshop. ‘Not as a workman,’ Dallmeyer replied. An interview with the great optician was soon arranged, and Dallmeyer was appointed scientific adviser to the firm, and entrusted with the testing and finishing of the highest class of optical apparatus. He so fully secured the confidence and approval of his employer that Mr. Ross gave his full consent to a marriage between Dallmeyer and his second daughter, Hannah Ross. In 1859 Andrew Ross died; he left to his son-in-law and co-worker a third of his large fortune, and that portion of his business which was concerned in the manufacture of telescopes. About this time Dallmeyer's name was first brought before the public by Sir John Herschel in the article on ‘Telescopes’ in the eighth edition of the ‘Encyclopædia Britannica,’ where he gives a list of the most important refracting telescopes then known, adding as to several that ‘Mr. Dallmeyer laid claim to the personal execution, and the computation of their curvatures.’ The largest object-glass for a telescope made by Dallmeyer did not exceed eight inches in diameter (his favourite size was 4⅛ inches), but all observers who have used his instruments concur as to their exquisite definition and perfection. This was due, in part, to his system of polishing the glass, an operation which he conducted underwater, thereby obtaining a ‘black’ polish seldom met with. Several of Dallmeyer's telescopes have been used in the government expeditions sent to observe eclipses of the sun and the transits of Venus. In 1861 Dallmeyer was elected a fellow of the Royal Astronomical Society, and he served for several years upon the council of the society. At the exhibition of 1862 Dallmeyer came to the front as a manufacturer of photographic lenses; and the greater part of his fame and fortune from this time rested on the admirable instruments which he supplied to photographers in all parts of the world, and of which more than thirty thousand had been sold up to the time of his death. His ‘triple achromatic lens’ is described by the jurors as ‘free from distortion, with chemical and visual foci coincident.’ This lens was specially valuable for copying, and architecture. Dallmeyer's portrait lenses were constructed on the principle of Professor Petzval, but in one modification, the relative positions of the flint and crown glass in the posterior combination are reversed, so as to render it possible, by slightly unscrewing them, to introduce spherical aberration at will and thus secure that ‘diffusion of focus’ preferred by many artists. In 1864 Dallmeyer patented a single wide-angle lens, which has since been largely used for photographing landscapes. It consists of two pieces of crown and one of flint glass worked to the proper curves and cemented together so as to form a meniscus of rather deep curvature. Dallmeyer was for many years a prominent member of the Royal Microscopical Society, and his work in the construction of object-glasses for the microscope is well known and appreciated. His last important improvement was in the condenser used in the magic, or, as Dallmeyer preferred to call it, the optical lantern. This was effected at the request of an old friend and veteran photographer, the Rev. T. F. Hardwich. The new condenser consisted of a plano-convex combined with a double convex lens, one surface of the latter being nearly flat. To aid celestial photography Dallmeyer constructed a photo-heliograph for the Wilna observatory of the Russian government in 1863, for taking four-inch pictures of the sun. This instrument was a complete success, and the Harvard College observatory was supplied with a similar one in the following year. In 1873 orders for five photo-heliographs for the transit of Venus expeditions were executed for the English government. These gave four-inch pictures of the sun. They have since been fitted with new magnifiers so as to give pictures eight inches in diameter, and are now constantly employed in solar photography. At the various exhibitions at Dublin and Berlin (1865), Paris (1867 and 1878), and Philadelphia (1876), Dallmeyer's lenses received the highest awards. The French government bestowed on him the cross of the Legion of Honour, while Russia gave him the order of St. Stanislaus. The topographical departments of our own and other governments left the optical work of the instruments they ordered entirely in Dallmeyer's hands. Every instrument was tested by him personally before it left his establishment. Dallmeyer contributed several papers—chiefly on photographic optics—to various periodical. He wrote a practical pamphlet ‘On the Choice and Use of Photographic Lenses,’ which has passed through six editions. For many years he served on the council of the Photographic Society of Great Britain.

About 1880 Dallmeyer was forced to relinquish active work, and during the next few years he undertook several long journeys in search of health. He resided in a large mansion built by himself on an elevated spot at Hampstead. He died on board ship off the coast of New Zealand, on 30 Dec. 1883.

Dallmeyer was twice married, his second