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ARTS, SCIENCES, AND MISCELLANEOUS
ENLARGED AND IMPROVED.
THE SIXTH EDITION.
Illustrated with nearly six hundred Engravings.
INDOCTI DISCANT; AMENT MEMINISSE PERITI.
PRINTED FOR ARCHIBALD CONSTABLE AND COMPANY;
ICROSCOPE, an optical instrument, consisting objects appear larger than they do to the naked eye. Single microscopes consist of a single lens or mirror; or if more lenses or mirrors be made use of, they only serve to throw light upon the object, but do not contribute to enlarge the image of it. Double or compound microscopes are those in which the image of an object is composed by means of more lenses or mirrors than
For the principles on which the construction of microscopes depends, see OPTICS. In the present article, it is intended to describe the finished instrument, with all its varied apparatus, according to the latest improve ments; and to illustrate by proper details its uses and importance.
I. Of SINGLE Microscopes
THE famous microscopes made use of by Mr Leeuwenhoeck, were all, as Mr Baker assures us, of the single kind, and the construction of them was the most simple possible; each consisting only of a single lens set between two plates of silver, perforated with a small hole, with a moveable pin before it to place the object on and adjust it to the eye of the beholder. He informs us also, that lenses only, and not globules, were used in every one of these microscopes.
1. The single microscope now most generally known cecxxxvII. and used is that called Wilson's Pocket Microscope. The Fig. 1. body is made of brass, ivory, or silver, and is represented by AA, BB. CC is a long fine threaded male screw that turns into the body of the microscope; D a convex glass at the end of the screw. cave round pieces of thin brass, with holes of different diameters in the middle of them, are placed to cover the above-mentioned glass, and thereby diminish the aperture when the greatest magnifiers are employed. EE, three thin plates of brass within the body of the microscope; one of which is bent semicircularly in the middle, so as to form an arched cavity for the reception of a tube of glass, the use of the other two be ing to receive and hold the sliders between them. F, a piece of wood or ivory, arched in the manner of the semicircular plate, and cemented to it. G, the other end of the body of the microscope, where a hollow female screw is adapted to receive the different magnifiers. H is a spiral spring of steel, between VOL. XIV. Part I.
the end G and the plates of brass, intended to keep the plates in a right position and counteract the long screw CC. I is a small turned handle, for the better holding, of the instrument, to screw on or off at plea
To this microscope belong six or seven magnifying glasses: six of them are set in silver, brass, or ivory, as in the figure K; and marked 1, 2, 3, 4, 5, 6, the lowest numbers being the greatest magnifiers. Lis the seventh magnifier, set in the manner of a little barrel, to be held in the hand for the viewing of any larger object. M is a flat slip of ivory, called a slider, with four round holes through it, wherein to place objects between two pieces of glass or Muscovy talc, as they appear at dddd. Six such sliders, and one of brass, are usually sold with this mioroscope, some with objects placed in them, and others empty for viewing any thing that may offer: but whoever pleases to make a collection, may have as many as he desires. The brass slider is to confine any small object, that it may be viewed without crushing or destroying it. N is a tube of glass contrived to confine living objects, such as frogs, fishes, &c. in order to discover the circulation of the blood. All these are contained in a little neat box of fish-skin or mahogany, very convenient for carrying in the pocket.
When an object is to be viewed, thrust the ivory slider, in which the said object is placed, between the two flat brass plates EE: observing always to put that side of the slider where the brass rings are farthest from the eye. Then screw on 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 CC, till your object be brought to suit your eye; which will be known by its appearing perfectly distinct and clear. It is most proper to look at it first through a magnifier that can show the whole at once, and afterwards to inspect the several parts more particularly with one of the greatest magnifiers; for thus you will gain a true idea of the whole, and of all its parts. And though the greatest magnifiers can show but a minute portion of any object at once, such as the claw of a flea, the horn of a louse, or the like; yet by gently moving the slider which contains the object, the eye may gradually examine it all over.
As objects must be brought very near the glasses when the greatest magnifiers are made use of, be careful not to scratch them by rubbing the slider against them