Fig. 4, K, a concave speculum of polished silver, in the center of which a lens is placed. On the back of this speculum a male screw, L, is made to fit the brass ring I, Fig. 3. Four of these specula of different concavities, with four glasses of different magnifying powers, as the objects may require. The greatest magnifiers have the least apertures. M, a round object plate, one side white and the other black, intended to render objects the more visible, by placing them, if black, upon the white, and if white, on the black side. A steel spring, N, turns down on each side, to secure any object; from the object plate there is a hollow pipe, to screw it on the needle’s point G, Fig. 3. O, a small box of brass, with a glass on each side, to confine any living object in order to examine it, having a pipe to screw upon the end of the needle at G. P, an ivory handle. Q, a pair of pliers to take up any object. R, a soft hair brush. To view any object, screw the speculum, with the magnifier you intend to use, into the brass ring, I; place your object either on the needle G, in the pliers H, on the object plate M, or in the brass hollow box O, as may be most convenient; then holding up your instrument by the handle P, look against the light through the magnifying lens, and by means of the nut, D, together with moving of the needle at its lower end, the object may be turned about, raised or depressed, brought nearer the glass, or put farther from it, till you have the true focal distance, and the light be seen reflected from the speculum strongly upon the object.[35] [35] Opake microscopes are now constructed more elegantly and simply. The chief merit of Wilson’s microscope appears, in being particularly adapted to minute objects, and these principally of the transparent kind; the barrel form is useful for excluding adventitious light. Excepting these peculiarities, its general utility is considered far short of the universal pocket microscope hereafter to be described. EDIT. OF ELLIS’S SINGLE OR AQUATIC MICROSCOPE. Plate VII. B. This instrument takes its name from Mr. John Ellis, author of “An Essay towards a Natural History of Corallines,” and of the “Natural History of many curious and uncommon Zoophytes.” By this instrument he was enabled to explain many singularities in the œconomy and construction of these wonderful productions of nature. To the practical botanist this instrument is recommended by the respectable authority of Mr. Curtis, author of the Flora Londinensis, a work which does credit to the author and the nation. This microscope is simple in its construction, easy in its use, and very portable; these advantages, as well as some others which it also has over other portable microscopes, have accelerated the sale thereof, and caused it to be very much adopted. DESCRIPTION OF THE VARIOUS PARTS OF THE MICROSCOPE.