ENCYCLOPÆDIA BRITANNICA.

OR, A

DICTIONARY

OF

ARTS, SCIENCES, AND MISCELLANEOUS

LITERATURE;

ENLARGED AND IMPROVED.

THE SIXTH EDITION.

Jllustrated with nearly sir hundred Engravings.

VOL. XIV.

INDOCTI DISCANT; AMENT MEMINISSE PERITI.

EDINBURGH:
PRINTED FOR ARCHIBALD CONSTABLE AND COMPANY;

AND HURST, ROBINSON, AND COMPANY, 90, CHEAPSIDE,

LONDON.

1823.

Microscope.

M

sure.

a

of lenses, or mirrors, by ineans of wbich smali the plates in a right position and counteract the long scupe. v objects appear larger than they do to the naked eye. screw CC. I is a small turned bandle, for the better

Single microscopes consist of a single lens or mirror; or holding of the instrument, to screw on or off at pleaif more lenses or mirrors be made use of, they only serve to throw light upon the object, but do not contribute to To this microscope belong six or seven magnifying enlarge the image of it. Double or compound mir glasses : six of them are set in silver, brass, or ivory, croscopes are these in which the image of an object is as in the figure K ; and marked 1, 2, 3, 4, 5, 6, the composed by means of more leases or mirrors than lowest numbers being the greatest magnifiers. L is one.

the seventh magnifier, set in the manner of a little For the principles on which the construction of mi barrely to be beld in the hand for the viewing of any

, croscopes depends, see Optics. In the present article, larger object. M is a flat slip of ivory, called a

, at is intended to describe the finished instrument, with slider, with four round holes through it, wherein to

, all its varied apparatus, according to the latest improve place objects between two pieces of glass or Muscovy ments; and to illastrate by proper details its uses and talc, as they appear at d d d d. Six such sliders, and importance.

one of brass, are usually sold with this mioroscope,

some with objects placed in them, and others empty I. Of Single Microscopes.

for viewing any thing that may offer : but whoever

pleases to make a collection, may have as many as he The famous microscopes made use of by Mr Leeu- desires. The brass slider is to confine any small ubject, Penhoeck, were all, as Mr Baker assures us, of the that it may be viewed without crushing or destroying single kind, and the construction of them was the most it. N is a tube of glass contrived to confine living obsimple possible; each consisting only of a single lens set jects, such as frogs, tishes, &c. in order to discover the between two plates of silver, perforated with a small circulation of the blood. All these are contained in a hole, with a moveable pin before it to place the object little neat box of fish-skin or mahogany, very convenient on and adjust it to the eye of the beholder. He informs for carrying in the pocket. us also, that lenses only, and not globules, were used in When an object is to be viewed, thrust the ivory every one of these microscopes.

slider, in which the said object is placed, between the Plate 1. The single microscope now most generally known two fat brass plates EE: observing always to put CCCXXXVII

. and used is that called Wilson's Pocket Alicroscope. The that side of the slider where the brass rings are far· Fig. To body is made of brass, ivory, or silver, and is repre- thest from the eye. Then screw on the magnifying

sented by AA, BB. CC is a long fine threaded male glass you intend to use, at the end of the instrument screw that turns into the body of the microscope ; D G; and looking through it against the light, turn the a convex glass at the end of the screw. Two con- long screw CC,

till your object be brought to suit cave round pieces of thin brass, with holes of different eye; which will be known by its appearing perfectly diameters in the middle of them, are placed to cover distinct and clear. It is most proper to look at it first the above-mentioned glass, and thereby diminish the through a magnifier that can show the whole at once, aperture when the greatest magnifiers are employed. and afterwards to inspect the several parts more partiEE, three thin plates, of brass within the body of the cularly with one of the greatest magnifiers ; for thus microscope ; one of which is bent semicircularly in the you will gain a true idea of the whole, and of all its middle, so as to form an arched cavity for the recep parts. And though the greatest magnifiers can show tion of a tube of glass, the use of the other two be- but a minute portion of any object at once, such as the ing to receive and hold the sliders between them. F, claw of a Hea, the horn of a louse, or the like ; yet by a piece of wood or ivory, arched in the manner of gently moving the slider which contains the object, the the semicircular plate, and cemented to it. G, the eye may gradually examine it all over. other end of the body of the microscope, where a hol- As objects must be brought very near the glasses low female screw is adapted to receive the different when the greatest magnifiers are made use of, be caremagnifiers. H is a spiral spring of steel, between ful not to scratch them by rubbing the slider against VOL. XIV. Part I.

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