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.