exterior tube or case, in which the other slides up and down in an easy and steady manner. This motion of the tube C is useful to increase or decrease the magnifying power of the body-glass when thought necessary, as before mentioned. E is a pipe or snout screwed on to the body of the microscope D, and at its lower part, over the several magnifying lenses hereafter described. FGHI is the square stem of the microscope, upon which the stage R moves in an horizontal position, upwards or downwards, by means of the fine rackwork of teeth and pinion. KL is a strong solid joint and pillar, by which the position of the instrument is readily altered from a vertical one to an oblique or to a perfectly horizontal one, as may be required; it is thus well adapted to the ease of the observer either sitting or standing; and as it is very often convenient to view objects by direct unreflected light, when the square stem FI is placed in an horizontal position for this purpose, the mirror T is then to be taken off in order to prevent the obstruction of the rays. M is a circular piece of brass, serving as a base to the pillar. NOP, the tripod or foot by which the whole body of the microscope is steadily supported; it folds up when packed into the case. W is a brass frame, that contains the condensing lens, and acts in conjunction with the large concave and plane mirrors below at T; the reflected rays from which, either of the common light or of that of a candle or lamp, it agreeably modifies, and makes steady in the field of view.

The particulars of the apparatus to this microscope are as follow: Q is a circular brass box, containing six magnifiers or object lenses, numbered 1, 2, 3, 4, 5, 6; the digits of which appear severally through a small round hole in the upper plate of it. To the upper side is fixed a small circle of brass, by which it is connected with, and screwed into, the round end of the arm abcd; which is a long piece of brass, and moves through either by teeth or pinion, or not, as may be desired, in ef; which is a socket on the upper part of the pillar, and admits, with a motion both easy and steady, the brass arm. R is a fixed stage, upon which the objects to be viewed are to be placed; it is firmly fastened to the square pillar, which is moved by the rackwork. In the middle is a large circular hole, for receiving concave-glasses, with fluids, &c. it has also a sliding spring-frame to fasten down slips of glass or other things: at a b c are three small sockets or holes, intended to receive several parts of the apparatus. S is the refractor, or illuminating lens, for converging the sun's rays upon opaque objects laid upon the stage R. To this purpose it moves on a semicircle upon a long shank g, in a spring socket h, in the arm i; this arm moving every way by a stout pin k in the socket a of the stage. In this manner it is easily adjusted to any position of the sun, candle, &c.-T, the reflecting-glass frame, containing a concave and plane speculum, which is moved upon the square pillar by the hand. The use of it is to illuminate all transparent objects that are applied to the stage above.

Fig 14, plate 110, No 1, is an auxiliary moveable stage; which by means of a pin k is placed in the hole a of the stage R, and can be moved in an horizontal direction over the whole field of the stage. In this stage there are three circular holes with shouldered bottoms: a large one in the middle, and on each side a small one, for the reception of the three following necessary articles: No 2, a watchglass to be placed in the large hole, to hold fluids containing animalcules, &c.; a circular piece of ivory, No 3, one side of which is black, the other

white, to support opaque objects of different contrasted colours; and circular plane and concave glasses, No 4, for extemporaneous transparent objects-The same use is made of the other small hole as of the large one, only in a lesser degree, to receive small concave glasses, plates, &c.

No 5, is the silvered speculum, called a liberkuhn, which makes the single opaque microscope, by being screwed to the slider a bed (fig. 13. instead of the box of lenses Q, and the body A E above it. The chief use of this is to view very small objects strongly illuminated near the compounded focus of the mirror T (fig. 13.) No 6, is the forceps, or pliers, for holding such kind of objects, and by which they can be applied very readily to the focus of the lens in the liberkuhn. They have a motion all ways by means of the spring socket a, the joint b, and the shank c; they are placed in the socket c of the fixed stage R (fig. 13.). No 7, is a small piece of ivory, to be placed upon the pointed end of the pliers; it is black upon one side, and white upon the other, to receive opaque objects.

No 8, is a liberkuhn of a larger size than that first mentioned, with a hole in its centre: this is screwed into No 9, the hole a of a brass ring, fastened to a long wire b; which moves up and down in the spring socket b of the stage R, in which it also moves sideways; and thus, with the body AE above, forms an aquatic compound microscope for showing all sorts of objects in water and other fluids placed under it in the watch-glass No 2,on the stage.

No 11, is a cone with a proper aperture a to exclude superfluous light, that would disturb a critical observation of a curious object; it is placed on the under side of the fixed stage R.

No 12, is what is usually called a bug-box, consisting of a concave glass with a plane one screwed over it; by means of which a bug, louse, flea, &c. may be secured and viewed alive. It is to be placed on either of the stages R (fig. 13.), or No 1 (fig. 14.).

No 13, is the fish-pan. In the long concave body ab, a fish may be so confined by the ribband c, that the transparent tail may be in part over the slit or hole at a. In this state, it is placed on the stage R, with the pin d in the hole c of the stage, and moves freely and horizontally for viewing the circulation of the blood, &c.

No 14, is the slider-holder that is placed on the stage R: it receives the sliders and tubes when filled with transparent objects, to be viewed either by the compound or single microscope.

No 15, represents the ivory slider, to hold the objects between the tales as usual.

No to, is a useful auxiliary slider framed in brass. In this slider small concave glasses are cemented; and a slip of plane glass slides over them; by which any small living object, as mites, &c. may be confined without injury, and deliberately viewed.

No 17, represents a set of glass tubes, three in number, one within another; they are useful for small tadpoles, water-newts, eels, &c. when the circulation of the blood is to be viewed. There is a small hole at one end of each tube, that serves to admit the air; for, when they are filled with water, the other end is stopped with a cork.

No 18, is a small ivory box, containing spare tales and wires, to supply the sliders with occasionally.

No 19, a brass cell or button, containing a very small lens, properly set between two small plates of brass, that it may be brought very near to the object when viewed therewith as a single microscope.

a scroll of brass fixed upright upon a roun wooden base B, or mahogany drawer or case, so as to stand perfectly firm and steady. C is a brass screw, that passes through a hole in the upper limb of the scroll into the side of the microscope D, and screws it fast to the said scroll. E is a concave speculum set in a box of brass, which hangs in the arch G by two small screws ff, that screw into the opposite sides thereof. At the bottom of this arch is a pin of the same metal, exactly fitted to a hole in the wooden pedestal, made for the reception of the pin. As the arch turns on this pin, and the speculum turns on the end of the arch, it may, by this twofold motion, be easily adjusted in such a manner as to reflect the height of the sun, of the sky, or of a candle, directly upwards through the microscope that fixed perpendicularly over it; and by so doing may be made to answer many purposes of the large double reflecting microscope. The body of the microscope may also be fixed horizontally, and objects viewed in that position by any light you choose, which is an advantage the common double reflecting microscope has not. It may also be rendered further useful by means of a slip of glass; one end of which being thrust through between the plates where the sliders go, and the other extending to some distance, such objects may be placed thereon as cannot be applied in the sliders: and then, having a limb of brass that may fasten to the body of the microscope, and extend over the projecting glass a hollow ring wherein to screw the magnifiers, all sorts of subjects may be examined with great convenience, if a hole be made in the pedestal, to place the speculum exactly underneath, and thereby throw up the rays of light. "The pocket-microscope, thus mounted (says Mr. Baker), is as easy and pleasant in its use, as fit for the most curious examination of the animalcules and salts in fluids, of the farinæ in vegetables, and of the circulation in small animals; in short, is as likely to make considerable discoveries in objects that have some degree of transparency, as any microscope I have ever seen or heard of"

The brass scroll A is now generally made to unscrew into three parts, and pack with the microscope and apparatus into the drawer of a mahogany pocket-case, upon the lid of which the scroll is made to fix when in use.

The opaque apparatus also, as above described, is applicable this way by reflection. It only consists in turning the arm R (fig. 1.), with the magnifier over the concave speculum below (fig. 2.), or to receive the light as reflected obliquely from it the silver speculum screwed into R will then reflect the light, which it receives from the glass speculum strongly upon the object that is applied upon the wire T underneath.

This microscope, however, is not upon the most convenient construction, in comparison with others now made: it has been esteemed for many years past from its popular name and recommendation by its makers. Its portability is certainly a great advantage in its favour; but in most respects it is superseded by the microscopes hereafter described.

3. Microscope for Opaque Objects, called the Single Opaque Microscope. This microscope remedies the inconvenience of having the dark side of an object next the eye, which formerly was an insurmountable objection to the making observations on opaque Sects with any considerable degree of exactness faction: for, in all other contrivances com

monly known, the nearness of the instrument to the object (when glasses that magnify much are used) unavoidably overshadows it so much, that its appearance is rendered obscure and indistinct And, notwithstanding ways have been tried to point light upon an object, from the sun or a candle, by a convex glass placed on the side thereof, the rays from either can be thrown upon it in such an acute angle only, that they serve to give a confused glare, but are insufficient to afford a cierr and perfect view of the object. But by this mi croscope, by means of a concave speculum of silver highly polished, in whose centre a magnifying less is placed, such a strong and direct light is reflected upon the object, that it may be examined with all imaginable ease and pleasure. The several parts of this instrument, made either of brass or silva, are as follow:

Through the first side A, passes a fine screw, B, the other end of which is fastened to the more able side C. D is a nut applied to this screw, by the turning of which the two sides A and C are gradually brought together. E is a spring of steel that separates the two sides when the nut is unscrewed. F is a piece of brass, turning round in a socket, whence proceeds a small spring tube moving upon a rivet; through which tube there runs a steel wire, one end whereof terminates in a sharp point G, and the other with a pair of pliers H fastened to it. The point and pliers are to thrust into, or take up and hold, any insect or object; and either of them may be turned upwards, as best suits the purpose. I is a ring of brass, with a female screw within it, mounted on an upright piece of the same metal; which turns round on a rivel that it may be set at a due distance when the least magnifiers are employed. This ring receives the screws of all the magnifiers. K is a concave speculum of silver, poli hed as bright as possible; in the centre of which is placed a double convex lens, with a proper aperture to look through it. On the back of this speculum a male screw L is made ta fit the brass ring I, to screw into it at pleasure. There are four of these concave specula of r ent depths, adapted to four glasses of different magnifying powers, to be used as the objects to be examined may require. The greatest magnifiers have the least apertures. M is a round objectplate, one side of which is white and the other black the intention of this is to render objects the more visible, by placing them, if black, on the white side, or, if white, on the black side. A steel spring N turns down on each side to make any object fast; and issuing from the object-plate is a hollow pipe to screw it on the needle's point G. O is a smail box of brass, with a glass on each side, contrived to confine any living object in order to examine it: this also has a pipe to screw upon the end of the needle G. P is a turned handle of wood, to screw into the instrument when it is made use of. Q.a pair of brass pliers to take up any object, or manage it with conveniency R is a soft hair brush for cleaning the glasses, &c. S is a small ivory bex for tales, to be placed, when wanted, in the sull brass box O.

When you would view any object with this microscope, screw the speculum, with the Ifier you think proper to use, into the brass naz L Place your object, either on the needle G is its pliers H, on the object-plate M, or in the balles brass box O, as may be most convenient: then, holding up your instrument by the handle P, look against the light through the magnifying less: and by means of the nut D, together with the