Encyclopaedia Britannica [14, 4 ed.]

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MIC
MIC
MID
MID
MIG
MIL
MIN
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MIR
MOG
MON
MON
MOR
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ENCYCLOPEDIA

BRITANNICA.

Cnrpclopaetua

iSritanmca;

OR, A

DICTIONARY

OF

ARTS, SCIENCES, AND MISCELLANEOUS

LITERATURE;

ENLARGED AND IMPROVED.

THE FOURTH EDITION.

aUujStrateO tottl) neatlg sit {junureD cEngraWngs.

VOL. XIV.

INDOCTI DISCANT ; AMENT MEMINISSE PERITI,

EDINBURGH: Printed by Andrew Bell) the Proprietor) FOR ARCHIBALD CONSTABLE AND COMPANY, EDINBURGH J AND FOR VERNOR, HOOD, AND SHARPE, LONDON. 1810.

ENCYCLOPAEDIA BRITANNICA,

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Microfcope. "J\ /|" ICROSCOPE, an optical inflrument, confifting the end G and the plates of brafs, intended to keep Microfcope. JLVX of lenfes, or mirrors, by means of which fmall the plates in a right pofition and counteraft the long —v-—-' objects appear larger than they do to the naked eye. fcrew CC. I is a fmall turned handle, for the better Sing/e microfcepes confill: of a fingle lens or mirror ; or if holding of the inftrument, to fcrew on or off at pleamore lenfes or mirrors be made ufe of, they only ferve fure. to throw light upon the objeft, but do not contribute to To this microfcope belong fix or feven magnifying enlarge the image of it. Double or compound mi- glaffes : fix of them are fet in filver, brafs, or ivory, crofcopes are thofe in which the image of an object is as in the figure K ; and marked i, 2, 3, 4, 5, 6, the eompofed by means of more lenfes or mirrors than loweft numbers being the greateft magnifiers. L is one. the feventh magnifier, fet in the manner of a little For the principles on which the conftru&ion of mi- barrel, to be held in the hand for the viewing of any crofcopes depends, fee OPTICS. In the prefent ar- larger object. M is a flat flip of ivory, called a ticle, it is intended to defcribe the finilhed inftrument, fider, with four round holes through it, wherein to with all its varied apparatus, according to the lateft im- place objefts between turn pieces of glafs or Mufcovy provements ; and to illuftrate by proper details its ufes talc, as they appear at dddd. Six fuch Aiders, and and importance. one of brafs, are ufually fold with this microfcope, fome with objedls placed in them, and others empty I. Of SINGLE Microfcopes. for viewing any thing that may offer : but whoever pleafes to make a colledlion, may have as many as he THE famous microfcopes made ufe of by Mr Leeudefires. The brafs Aider is to confine any fmall obje£l, w^enhoeck, W'ere all, as Mr Baker affures us, of the that it may be viewed without cruftiing or deftroying Tingle kind, and the conftruftion of them was the moft it. N is a tube of glafs contrived to confine living obiimple poflible ; each confifting only of a fingle lens fet jefts, fuch as frogs, fifties, &c. in order to diicover between two plates of filver, perforated with a fmall the circulation of the blood. All thefe are contained hole, with a moveable pin before it to place the ob- in a little neat box of fifti-fldn or mahogany, very conjeft on and adjuft it to the eye of the beholder. He venient for carrying in the pocket. informs us alfo, that lenfes only, and not globules, were When an object is to be viewed, thruft the ivory uied in every one of thefe microfcopes. Aider, in which the faid objeift is placed, between the Plate i. The fingle microfcope now moft generally known twm flat brafs plates EE : obferving always to put cccxxxvn. and ufed is that called Wilfon's Pocket Microfcope. The that fide of the Aider where the brafs rings are farbody is made of brafs, ivory, or filver, and is repre- theft from the eye. Then fcrew on the magnifying fented by AA, BB. CC is a long fine=threaded male glais you intend to ufe, at the end of the inftrument fcrew that turns into the body of the microfcope ; D G ; and looking through it againft the light, turn the a convex glafs at the end of the fcrew. Twm con- long fcrew CC, till your objeift be brought to fuit your cave round pieces of thin brafs, with holes of different eye ; which will be known by its appearing perfe6fly diameters in the middle of them, are placed to cover diftinft and clear. It is moft proper to look at it firft the above mentioned glafs, and thereby diminifti the through a magnifier that can ftiow the whole at once, aperture when the greateft magnifiers are employed. and attenvards to infpeft the feveral parts more partiEE, three thin plates of brafs within the body of the cularly with one of the greateft magnifiers \ for thus microfcope ; one of which is bent femicircularly in the you will gain a true idea of the whole, and of all its middle, fo as to form an arched cavity for the recep- parts. And though the greateft magnifiers can ftiow tion of a tube of glafs, the ufe of the other two be- but a minute portion of any objedl at once, fuch as the ing to receive and hold the Aiders between them. F, claw ol a flea, the horn of a loufe, or the like ; yet by a piece of wood or ivory, arched in the manner of gent1^ moving the Aider which contains the objeil, the the femicircular plate, and cemented to it. G, the eye may gradually examine it all over. other end of the body of the microfcope, where a holAs objefts murt be brought very near the glaffes low female fcrew is adapted to receive the different when the greateft magnifiers are made ufe of, be caremagnifiers. H is a fpiral fpring of fteel, between ful not tp fcratch them by rubbing the Aider againft VOL. XIV. Part I. A them

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Microfcepe. them as you move it in or out. A few turns of the v fcrew CC will eafily prevent this mifchief, by giving them room enough. You may change the objeds in your Aiders for any others you think proper, by taking out the brafs rings with the point of a penknife j the talcs will then fall out, if you but turn the Aiders j and after putting what you pleafe between them, by replacing the brafs rings you will faften them as they were before. It is proper to have fome Aiders furniAied with talcs, but without any obje£t between them, to be always in readinefs for the examination of Auids, falls, fands, powders, the farina of flowers, or any other cafual objefts of fuch fort as need only be applied to the outfide of the talc. The circulation of the blood may be eafieft feen in the tails or fins of fiflies, in the fine membranes between g frog’s toes, or beft of all in the tail of a water-newt. If your objeft be a fmall fifli, place it within the tube N, and fpread its tail or fin along the fide thereof: if a frog, choole fuch a one as can but juft be got into your tube *, and, with a pen, or fmall ftick, expand the tranfparent membrane between the toes of the frog’s hind foot as much as you can. When your objedl is fo adjufted that no part of it can intercept the light from the place you intend to view, unfcrew the long fcrew CC, and thruft your tube into the arched cavity, quite through the body of the microfcope ; then fcrew it to the true focal diftance, arid you will fee the blood palling along its veffels with a rapid motion, and in a moft furprifing manner. The third or fourth magnifiers may be ufed for frogs or fifties : but for the tails of water-newts, the fifth or fixth will do $ becaufe the globules of their blood are twice as large as thofe of frogs or fifli. The firft or fecond magnifier cannot well be employed for this purpofe j becaufe the thicknefs of the tube in which the objedt lies, will fcarce admit its being brought fo near as the focal diftance of the magni: fkr. An apparatus for the purpofe of viewing opaque, objedts generally accompanies this microfcope ; and which confifts of the following parts. A brals arn\ QR, which is fcrewed at Q, upon the body of the microfcope at G. Into the round hole R, any of the^ magnifiers fuitable to the objedl to be viewed are to. be fcrewed j and under it, in the fame ring, the concave poliftied filver fpeculum S. Through a fmaH aperture in the body of the microfcope under the brafs plates EE, is to Aide the long wire with thq forceps T : This wire is pointed at one of its ends; and fo, that either the points or forceps may be ufed ' for the objedts • as may be neceflary. It is eafy to conceive, therefore, that the arm at R, which turns, by a twofold joint at# and b, may be brought with its magnifier over the objedt, the light reAedted upon it by the application of the fpeculum, and the true, focus obtained by turning of the male fcrew CC as before diredted.— As ol jedts are fometimes riot'well fixed for view, either by the forceps, or .point,; the imall piece thown at V is added, and in. fuch cafes anfwers better : it fcrews over the point of TiCcuntains a fmall round piece of ivory, blackened on one fide, and left white upon the other as a contraft to coloured objedts, and by a fmall piece of vvatch-fpring fallens down the objedts upon the ivory.

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2. Sing/e Micr^ofcope by refleElion. In fig. 2. A is a Microfcope.. fcroll of brafs fixed upright upon a round wooden —Y—”J bafe B, or mahogany drawer or cafe, fo as to ftand perfedtly firm and fteady. C is a brafs fcrew, that paffes through a hole in the upper limb of the fcroll into the fide of the microfcope D, and fclews it faft to the faid fcroll. E is a concave fpeculum fet in a box of brafc, which hangs in the arch G by two fmall fcrews ff that fcrew into the oppolite fides thereof. At the bottom of this arch is a pin of the fame metal, exadlly fitted to a hole h in the wooden pedeftal, made . for tire reception of the pin. As the arch turns on this pin, and the fpeculum turns on the end of the arch, it may, by this twofold motion, be eafily adjufted in fuch a manner as to refledl the light of the fun, of the fky, or of a candle, diredtly upwards through the microfcope that is fixed perpendicularly over it j and by fo doing may be made to anfwer many purpofes of the large double refle&ing microfcope. The body of the microfcope may alfo be fixed horizontally, and obje£ls viewed in that pofition by any light you choofe; which is an advantage the common double, reflefting microfcope has not. It may alfo be rendered further ufeful by means of a flip of glafs $ one end of which being thruft through between the plates where the Aiders go, and the other extending to fome diftance^ fuch o! je£ls may be placed thereon as cannot be applied in the Aiders : and then, having a limb of brafs that may faften to the body of the microfcope, and ex.-, tend over the projecting glafs a hollow ring wherein to fcrew the magnifiers, all forts of fubjefts may be examined with great convenience, if a hole be made in the pedeftal, to place the fpeculum exaftly underneath, and thereby throw up the rays of, light. The pocketmicrofcope, thus mounted, fays Mr Baker, “ is as eafy and pleafant in its ufe ; as fit for the moft curious examination of the animalcules and falls in fluids, of the. farinae in vegetables, and of the circulation in fmall animals; in fliort,, is as likely to make conflderable difco.veries in objeCts that have fome degree of tranfparency, as, any microfcope I have ever feen or heard of.” The brafs fcroll A is now generally made to unferew into three parts, and pack with the microfcope and apparatus into the drawer of a mahogany pocketcafe, upon the lid of which the fcroll is made to fix when in ufe. The opaque apparatus alfo, as above deferibed, is applicable this way by refledion. It only confifts in turning the arm R (fig. I.), with the magnifier over the concave fpeculum below (fig. 2.), or to receive the light as reflected obliquely from it : the filver fpeculum fcrewed into R will then refleCt the light, which it receives from the glafs fpeculum, ftrongly upon the objeCt that is applied upon the wire T underneath. This microfcope,, however, is not upon the moft convenient conftruCtion,, in comparifon with others:now made: it has been efteemed for many years paft from its popular name, and recommendation by its makers. Its portability is certainly a great advantage in its favour ; but in moft refpeCts it is fuperfeded by the microfcopes hereafter deferibed. 3. Microfcope for Opaque Obje&s, called the Single Fig- 3. Oppque Microfcope. This microfcope remedies the inconvenience of having the dark fide of an objeCI next the

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Microfcope. tlie eye, which formerly was an infmmountable objedlion to the making obfervations on opaque objcdts with any confiderable degree of exaftnefs or fatisfaction : for, in all other contrivances commonly known, the nearnefs of the inftrument to the object (when glaffes that magnify much are ufed') unavoidably overihadows it fo much, that its appearance is rendered obfcure and indiflindt. And, notwithftanding ways have been tried to point light upon an objedt, from the fun or a candle, by a convex glafs placed on the fide thereof, the rays from either can be throtvn upon it in fuch an acute angle only, that they ferve to give a confufed glare, but are infufficient to afford , a clear and perfedt view of the objedt. But this microfcope, by means of a concave fpeculum of filver highly polilhed, in whofe centre a magnifying lens is placed, fuch a ftrong and diredl light is refledfed upon the objedt, that it may be examined with all imaginable eafe and pleafure. The feveral parts of this inftrument, made either of brafs or filver, are as follow. Through the firft fide A, paffes a fine fcrew B, the other end of which is faftened to the moveable fide C. D is a nut applied to this fcrew, by the turning of which the two fides A and C are gradually brought together. E is a fpring of fteel that feparates the two fides wThen the nut is unfcrewed. F is a piece of brafs, turning round in a focket, whence proceeds a fmall fpring tube moving upon a rivet ; through which tube there runs a fteel wire, one end whereof terminates in a ftiarp point G, and the other writh a pair of . pliers H faftened to it. The point and pliers are to thruft into, or take up and hold, any infedl or objedt ; and either of them may be turned upwards, as beft fuits the purpofe. I is a ring of brafs, with a female fcrew within it, mounted on an upright piece of the fame metalwhich turns round on a rivet, that it may be let at a due riiitance when the leaf! magnifiers are employed. This ring receives the fcrews of all the magnifiers. K is a concave fpeculum of filver, polilhed as bright as poflible ■, in the centre of which is placed a double convex lens, with a proper aperture to look through it. On the back of this fpeculum a male fcrew L is made to fit the brafs ring I, to fcrew into it at pleafure. Theie are four of thefe concave Ipecula of different depths, adapted to four glaifes of different magnifying powers, to be ufed as the objedis to be examined may require. The greateft magnifiers have the leaft apertures. M is a round objedtplate, one fide of which is w’hite and the other black : The intention of this is to render objedfs the more vifible, by placing them, if black, on the white fide, or, if white, on the black fide. A feel fpring N turns dowm on each fide to make any objedf fall; and iffuing from the objedl-plate is a hollowr pipe to fcrew it on the needle’s point G. O is a fmall box of brafs, with a glafs on each fide, contrived to confine any living objedl, in order to examine it : this alfo has a pipe to fcrew upon the end of the needle G. P is a turned handle of wood, to fcrew into the inftrument W’hen it is made ufe of. Q, a pair of brafs pliers to take up any objedl, or manage it with conveniency. R is a foft hair-brufh for cleaning the glaffes, &c. S is a fmall ivory box for talcs, to be placed, when wanted, in the fmall brafs r O. When you would view any objedf with this micro-

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fcope, fcrew the fpeculum, with the magnifier you Mhrofcope. think proper to ufe, into the brafs ring I. Place your “* objedl, either on the needle G in the pliers H, on the objedl-plate M, or in the hollow brafs box O, as may be moil convenient: then holding up your inftrument by the handle P, look againft the light through the magnifying lens; and by means of the nut D, together wdth the motion of the needle, by managing its lower end, the objedl may be turned about, raifed, or depreffed, brought nearer the glafs, or removed farther from it, till you find the true focal diflance, and the light be feen ftrongly refledled from the fpeculum upon the objedt, by which means it will be fhown in a manner lurprifingly diftindt and clear} and for this purpofe the light of the fky or of a candle w ill anfwer very well. Tranfparefit objedts may alfo be viewed by this microfcope ; only obferving, that when fuch come under examination, it will not always be proper to throw on them the light refledled from the fpeculum j for the light tranfmitted through them, meeting the refledted light, may together produce too great a glare. A little pradtice, however, will fhow how to regulate both lights in a proper manner. 1 4. Ellis' s Jingle and Aquatic Microfcope. Fig. 4. re-Fig. 4, prefents a very convenient and uleful microfcope, contrived by Mr John Ellis, author of An Effay upon Co-* rallines, &c. To pradlical botanifts, obfervers of animalcula, &c. it poffeffes many advantages above thofe juft deferibed. It is portable, fimple in its conftruction, expeditious, and commodious in ufe. K reprefents the box containing the whole apparatus : it is generally made of filh-lkin ; and on the top there is a female fcrew, for receiving the fcrew that is at the bottom of the pillar A : this is a pillar of brafs, and is ferewed on the top of the box. D is a brafs pin which fits into the pillar ; on the top of this pin is a hollow' focket to receive the arm w’hich carries the magnifiers ; the pin is to be moved up and down, in order to adjuft the lenfes to their focal or proper diftance from the objedl. [A. B. In the reprefentations of this microfcope, the pin _D is delineated as palling through a focket at one fide of the pillar A j whereas it is ufual at prefent to make it pafs down a hole bored through the middle of the pillar.] E, the bar which carries the magnifying lens \ it fits into the focket X, which is at the top of the pin or pillar D. This arm may be moved backwards and forwards in the focket X, and fideways by the pin D j fo that the magnifier, which is ferewed into the ring at the end E of this bar, may be eafily made to traverfe over any part of the objedt that lies on the ftage or plate B. FF is a polilhed filver fpeculum, with a magnifying lens placed at the centre thereof, which is perforated for this purpofe. The filver fpeculum fcrews into the arm E, as at F. G, another fpeculum, with its lens, w'hicli is of a different magnifying power from the former. H, the femicircle which fupportsthe mirror 1 •, the pin R, affixed to the femicircle H, paffes through the hole which is towards the bottom of the pillar A. B, the ftage, or the plane, on which the objedts are to be placed ; it fits into the fmall dove tailed arm which is at the upper end of the pillar DA. C, a plane g’afs, with a fmall piece of black filk ftuck on it 5 this glafs is to lay in a groove made in the ftage C. M,' a hollow glafs to be laid occafionally on the ftage mA 2 ftead

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