One of the large lenses may occasionally be placed on the outer edge of the screen box, the other lens being taken out; the view on the rough glass is by these means magnified, and appears to greater advantage. But, besides the grey glass used in the former construction, there is a second in this, placed farther within the body, about half way; and, when the large lens is in the screen box, objects appear better in this than in the former way. It has a still greater effect upon those who are unacquainted with the nature of lenses, as it makes them judge the distance and magnitude much greater than they really are, and is therefore more pleasing than the grey glass in front. Only one grey glass can be used at a time; both being removed when opake objects are viewed. The stage, F, Fig. 5, is considerably different from that at C, Fig. 3; it is judged more convenient and commodious than the other, and serves, with a small alteration, for both transparent and opake objects. A truncated cone can also be here applied for cutting off superfluous rays of light occasionally. The method of illuminating the objects is also different. The mode now adopted answers better for opake and transparent objects, throws a stronger light, and is more convenient in application. It consists of two lenses, 1 and 2, Fig. 5; the larger one is to be placed at the end of the bar next the lamp. The smaller one to be adjusted so as to give a strong light. A third is also added, to be used occasionally with opake objects; it is to be applied close to the large lens. Experience will shew when it is to be used, or not. By moving the bar, G, on which these lenses are placed round the stage pillar, M, you bring it so much fronting the stage as effectually to enlighten opake objects by means of the lamp. The light thus afforded is received directly, and none lost by reflection. The objects are fixed on circular wheels of wood, see Fig. 7, the brass centers of which, are fitted to the hole, _b_, of the stage, Fig. 5; and about this center they are to be turned by the hand for the changing of the objects. As some objects, such as sections of wood, are seen to advantage both as transparent and opake, a frame containing a plane and a concave mirror is added to this instrument, serving two purposes: by bringing the bar to the front of the stage, removing the large lens, and putting the mirror in its place, the object may be viewed either way, without moving from the seat, by turning the instrument a little round. This experience will discover. The light of the sun may be thrown by the plane mirror on the condensing lens, so as to produce a strong full field of light on the grey glass. This has a grand effect when the large lens is at the end of the screen box, and could not be applied in this manner in former constructions. It becomes also an opake solar microscope, by turning the bar round to enlighten opake objects.