cradle joint, G, by which the instrument can be inclined by turning the screw-head, H (connected with an endless screw acting upon a worm-wheel). The arm, I, supporting the compound body, is supplied with a rack and pinion, K, by which it can be moved backwards and forwards, and a joint is placed below it, upon which the body can be turned into the horizontal position; another bar, carrying a stage and mirror, can be attached by a screw, L N, so as to convert it into a horizontal microscope. The stage, O, is provided with all the usual apparatus for clamping objects, and a condenser can be applied to its under surface; the stage itself may be removed, the arm, P, supporting it, turned round on the pivot, C, and another stage of exquisite workmanship placed in its stead, the under surface of which is shown at Q.” [Illustration: Fig. 3.--Martin’s Universal Microscope. 1782.] This stage is strictly a micrometer one, having rectangular movements and a fine adjustment, the movements being accomplished by the fine-threaded screws, the milled heads of which are graduated. The mirror, E, is a double one, and can be raised or depressed by rack and pinion; it is also capable of removal, and an apparatus for holding large opaque objects, such as minerals, can be substituted for it. The accessory instruments are very numerous, and amongst the more remarkable may be mentioned a tube, M, containing a speculum, which can take the place of the tube, R, and so form a reflecting microscope. The apparatus for holding animalcules or other live objects, which is represented at S, as well as a plate of glass six inches in diameter, with four concave wells ground in it, can be applied to the stage, so that each well may be brought in succession under the magnifying power. The lenses belonging to this microscope are twenty-four in number; they vary in focal length from four inches to one-tenth of an inch; ten of them are supplied with Lieberkuhns. A small arm, capable of carrying single lenses, can be supplied at T, and when turned over, the stage of the instrument becomes a single microscope; there are four lenses suitable for this purpose, their focal length varying from one-tenth to one-fortieth of an inch. The performance of all the lenses is excellent, and no pains appear to have been spared in their construction. There are numerous other pieces of accessory apparatus, all remarkable for the beauty of their workmanship.[4]