Essays on the Microscope / Containing a Practical Description of the Most Improved Microscopes, a General History of Insects, etc., etc.

by George Adams

To use the transparent solar microscope.

Fasten the square plate against the inside of a window-shutter, by the two screws O, P, which are to go from the outside of the window-shutter through it, and then be screwed into their respective holes in the square plate at G H I. The mirror is to be on the outside of the shutter, passing through a hole made for that purpose. Darken the room; then place a screen at about six or eight feet distance from the window, the farther it is from it the larger is the image: now move the mirror, K L, by the two nuts M N, till the sun’s rays come through the instrument in an horizontal direction to the screen, forming a round spot thereon; screw the microscope, Fig. 5, into its place E F; put the slider with the lenses, Fig. 8, at q, Fig. 5, and the object slider between the plates at h; adjust the object to the focus of the magnifying lens by the screw b, till the object appears distinct and clear on the screen. By moving the internal tube of the body, the object may be placed at different distances from the lens which is fixed at A B, so as to be sufficiently illuminated, and not burnt by the solar rays. If the screws O, P, are to pass inside the room, the two nuts, Fig. 12, must be previously fixed.

THE SCREW BARREL, OR WILSON’S SINGLE POCKET MICROSCOPE. [Plate II. B.] Fig. 1 and 2.

This microscope of Mr. Wilson’s is an invention of many years standing, and was in some measure laid aside, till Dr. Lieberkühn introduced the solar apparatus to which he applied it, there being no other instrument at that time which would answer his purpose so well; it is much esteemed in particular cases. The body of the microscope is represented at A B, Fig. 1, and is made either of silver, brass, or ivory. C C is a long fine-threaded male screw, that turns into the body of the microscope. D, a convex glass at the end of the said screw, on which may be placed, as occasion requires, one of the two concave apertures of thin brass to cover the said glass, and thereby diminish the aperture when the greatest magnifiers are used. E, three thin plates of brass within the body of the microscope, one whereof is bent to an arched cavity for the reception of a tube of glass. F, a piece of wood or brass, curved in the manner of the said plate, and fastened thereto. G, the other end of the microscope, where a female screw is adapted to receive the different magnifiers. H, a spiral spring of steel, between the said end, G, and the plates of brass, E, intended to keep the plates in a due position, and counteract against the long screw, C. I, a small ivory handle. To this microscope belong seven different magnifying glasses, six of which are set in cells, as in Fig. K, and are marked from 1, to 6: the lowest numbers to the greatest magnifiers. L is the seventh magnifier, set in the manner of a little barrel, to be held in the hand for viewing any large object. M is an ivory slider with the objects. Six of these, and one of brass, are usually sold with this microscope. There is also a brass slider not shewn in the figure, to confine any small object, that it may be viewed without crashing or destroying it. N, a pair of forceps, or pliers, for the taking up of insects or other objects, and applying them to the sliders or glasses. O, a camel hair brush, to take up and examine a small drop of liquid, brush the dust away, &c. P is a glass tube to confine living objects, such as frogs, fishes, &c.

When you view an object, push the ivory slider, in which the said object is placed, between the two flat brass plates, observing always to put that side of the slider, where the brass rings are, farthest from the eye; then screw in the magnifying glass you intend to use at the end of the instrument G, and looking through it against the light, turn the long screw, C C, till your object is brought to appear distinct, or to the true focal distance. To examine any object accurately, view it first through a magnifier that will shew the whole at once, and afterwards inspect the several parts more particularly with one of the greatest magnifiers; for thus you will gain a true idea of the whole, and all its parts: and, though the greatest magnifiers can shew but a minute portion of any object at once, such as the claw of a flea, the horn of a louse, &c. yet by gently moving the slider that contains your object, the eye will gradually see the whole; and if any part should be out of the focal distance, the screw, C C, will easily bring it to the true focus. As objects must be brought very near the glass, when the greatest magnifiers are used, be particularly careful not to rub the slider against the glasses as you move it in or out. A few turns of the screw, C C, will easily obviate this.

DESCRIPTION OF A SCROLL FOR FIXING WILSON’S POCKET MICROSCOPE, AND A MIRROR FOR REFLECTING LIGHT INTO IT.

A B C, Fig. 2, is a brass scroll, which, for the better conveniency of carriage, is made to unscrew into three parts, and may be put into the drawer upon which it stands, with its reflecting mirror D, and Wilson’s pocket microscope, G. The upper part of the scroll is taken off at B, by unscrewing half a turn of the screw; then, if lifted up, it will come out of the socket. The lower part unscrews at C, and the base at E. The mirror lifts out at F, which, with the scroll, lies in one partition of the box.

To apply this scroll for use, fix the body of the microscope to the top thereof by the screw, A, as in Fig. 2, by screwing it in the same hole as the ivory handle was applied to before. The brass or ivory slider being fixed as before described, and the microscope placed in a perpendicular position, move the mirror, D, in such a manner as to reflect the light of the sky, of the sun, or a candle, directly upwards through the microscope; by which means the object will be most conveniently viewed. It is further useful for viewing opake objects, by screwing the arm, Q R, Fig. 1, into the body of the microscope at G; then screwing into the round hole, R, that magnifier which you think will best suit your object, and putting the concave speculum, S, on the outside of the ring, R, you will observe in the body of the microscope, between the wood or brass, F, and the end of the male screw, C C, a small hole, u, through which slides the long wire, T, which has a point at one end, and forceps at the other, that may be used occasionally as your objects require. When you have fixed this, and your object on it, turn the arm, R, till the magnifier is brought over the object; it may be then adjusted to the true focus, by turning the screw, as before. It must also be brought exactly over the speculum, by turning the upper part of the scroll to one side, till your object and the two specula are in one line, as will be found by trial; and then fix it by the screw, B, at which time the upper surface of the object will be enlightened by the light reflected from the mirror, D, to the concave speculum.

DESCRIPTION OF A SMALL MICROSCOPE FOR OPAKE OBJECTS. [Plate II. B.] Fig. 3 and 4.

A, Fig. 3, is a fixed arm, through which passes a screw, B, the other end is fastened to the moveable arm, C. D, a nut fitted to the said screw, which, when turned, will either separate or bring together the two arms, A C. E, a steel spring, that separates the two sides when the nut is unscrewed. F, a piece of brass turning round in a spring socket, moving on a rivet, in which moves a steel wire pointed at the end G, and the other end a pair of pliers, H: these are either to thrust into, or take up and hold any object, and may be turned round as required. I, a ring of brass, with a female screw fixed on an upright piece of the same metal, turning on a rivet, that it may be set at a due distance when the least magnifiers are used, and is adapted to the screws of all the magnifiers.