A moveable stage, W, which by the pin, _a_, is applied to the hole, S, of the stage Fig. 2, and thereby has an horizontal motion under the whole field of view, without disturbing any other part of the instrument. To the large hole of this stage are fitted a deep concave glass, _r_, and the concave and plane glasses, _s_ and _o_; and to the small holes, _x_ _x_, a black and white piece of ivory, _w_, for opake objects, and a concave and plane glass similar to _o_ and _s_. An extra concave silver speculum with a less magnifier than the other, as shewn at _f_, used for the larger kind of opake objects, like the other, fitted to the arm C D, and used instead of the magnifiers in the wheel, P. Rack-work is sometimes cut in the arm C D, to turn the pinion above, so as to move the magnifiers in a linear direction over the objects in the most accurate degree; and also the stage N I S jointed, to turn by a screw and teeth in an horizontal direction at right angles to the above, thereby rendering a slow and accurate motion, perfectly suitable to the various positions of any living animal under examination. Six or more larger ivory sliders, with cuttings of different woods, &c. are also frequently added; but as these enhance the expense, and may be extended to the desire of the purchaser, his choice, and not my description here, will determine the extent of the apparatus to the microscope. When packed up into its mahogany, or black shagreen case, the outside dimensions are about twelve inches and an half long, nine inches broad, and three inches three-quarters deep. A microscope from this plan is frequently made of smaller dimensions, for the convenience of persons who frequently travel, and is contained in a fish-skin case about seven inches long, four inches and an half broad, and two inches deep, and is the most complete instrument of the sort. TO USE THIS MICROSCOPE. As in the former one, place the slider-holder K, with a slider of objects in it, in the stage N I S; move the arm C D, in its socket, so that a mark on the side is brought to the edge of the socket; then turn the arm till the magnifier is directly central over the object; look down the tube A B, and during that time, reflect the light strongly and clearly up into it from the mirror O below; and then, while you are looking through the body, gently turn the pinion at M to the right or left, till you see the object magnified in the most distinct and well-defined manner. Attending properly to this mode is the only care necessary to use any microscope whatsoever; and for want of doing which, many a beginner finds a difficulty in using properly his instrument. For price, see the list at the end.