In the ordinary physical apparatus Troughton made considerable improvement in the construction of the balance, and of the mountain barometer. In the same class may be mentioned the form given to the compensated mercurial pendulum; his pyrometer, by which some very valuable expansions have been determined; the apparatus by which Sir George Shuckburgh attempted to ascertain the standard of weight and measure; and that apparatus which, in the hands of Francis Baily, has given an invariable simple seconds pendulum. In the ordinary geodesical instruments Mr. Troughton greatly improved the surveying level and staff, and reduced them both in weight and price, with increased convenience and accuracy. It is, however, in the construction of astronomical instruments that this great mechanician particularly excelled; here he reigned without a rival. His portable astronomical quadrants are models of strength and lightness, while the repeating circle of Borda, an instrument which he disliked, first received its beauty and accuracy from his hands. The ordinary reading micrometer, and the position micrometer, commonly employed in the measurement of double stars, were greatly improved by him in simplicity and brought to perfection; and he first applied the former to dividing, though in circles and scales it had already been used in reading off. Mr. Troughton's larger works, such as his equatorial instruments, circles, transits, &c., are as well known in the astronomical world as those of Wren in the architectural; they are too numerous to mention here, and are distributed in various parts of the world. The gigantic zenith tube at Greenwich was about the last work on which he was engaged, and he had just time to finish it before his strength failed. The only astronomical instrument which is not greatly indebted to Mr. Troughton is the telescope, and he was deterred from making any attempt in this branch of his art by the curious physical defect of colour blindness, which existed in many members of his family. Like Dalton he could not distinguish colours, and had little idea of them, except generally as they conveyed the impression of greater or less light. The ripe cherry and its leaf were to him of one hue, only to be distinguished by their form. With this defect in his vision he never attempted any experiments in which colour was concerned; and it is difficult to see how he could have done so with success. The most remarkable of Troughton's writings are, 'An account of a method of dividing astronomical and other instruments by ocular inspection,' &c.--Phil. Trans., 1809, which was awarded with the Copley medal; 'A comparison of the repeating circle of Borda, with the altitude and Azimuth Circle'--Memoirs R. Ast. Soc.; and several articles in Brewster's 'Edinburgh Cyclopædia,' such as 'Circle,' 'Graduations,' &c.