Among the many ingenious novelties enumerated in his published papers we find the graduated lengthening of the body-tube of the microscope; a stage-fitting for clamping and rotating the object; a subsidiary stage; a dark-well, and a large disc to incline and rotate opaque objects; a ground-glass light moderator; a live-box with bevelled flat-glass plate; an erector-eye-piece; an adapter for using Wollaston’s camera lucida for microscopical drawing; and, above all, a combination of lenses to act as a condenser under the object (evidently the first approach to the present achromatic sub-stage condenser). The value of the erector-eye-piece for facilitating dissections under the microscope is not even yet sufficiently appreciated. Tully published a descriptive account of Lister’s microscope, the first one of which he made, and acknowledged his indebtedness to “Mr. Lister’s ingenuity and skill.” Shortly afterwards Lister made known his discovery of the two aplanatic foci in a double achromatic object glass, and gave verbal directions to the three principal makers of microscopes in London, James Smith, Andrew Ross, and Hugh Powell, for the future construction of the achromatic objective, all of whom were intent on the improvement of their several models. To the latter the Society of Arts awarded, in 1832, a medal for his improved mechanical stage movements, on the “Turrell system,” which Powell first constructed for Edmund Turrell. This stage was made to rotate completely on its optic axis by means of an obliquely-placed pinion acting on a bevelled rack on the inner face of the stage-ring supporting the mechanism. In 1834 Powell once more received a Society of Arts medal, “the Iris,” for improvements in the application of a new form of fine adjustment. About the same date (1835) Andrew Ross introduced the socket-carrier of the body-tube of the microscope on a strong stem, with rack bent in the middle, thus affording space for a larger stage. He likewise devised the hollow cross-bar, placed at right angles to the rack-stem, whereby he was enabled to use a new system of fine adjustment, consisting of a delicate screw with large milled head, acting by a point on the long arm of a lever, the short arm of which ends in a fork in contact with a stud placed on either side of a cylindrical sliding tube forming the nose-piece of the body-tube, and into which the objective is screwed. A spiral spring presses down the nose-piece, and against this the screw and lever act. This appears to have been the first really sensitive focussing method applied to the nose-piece; it was, and probably is, one of the most delicate systems ever applied to the microscope. It has enjoyed a long period of popularity, and I believe it still survives in Powell and Lealand’s instruments, which are very generally admitted to be of superior excellence for all purposes where extreme delicacy of focussing is an essential element.