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fig. 31.

Micro- rors,' one of which is plane, the other concave. These useful for any other objects that may be applied on Micro

mirrors may be moved in various directions, in order glasses fitted to the stage, as well as those put into the scope.
to reflect the light properly, by means of the pivots slider-bolder K. It is thereby not confined to this stage
on which they move, in the semicircle QSR, and the alone as in the preceding. When the body AB is
motion of the semicircle itself on the pin S: the con- taken away, the arm CD may be slipt away from its
cave mirror generally answers, best in the day-time; bar, with the magnifiers, and the forceps, wire, and
the plane mirror combines better with the condensing joint, applied to it; and it thereby serves the purpose
lens, and a lamp or candle. At D there is a socket for of a small single or opaque band microscope, for
receiving the pin of the arm Q (fig. 31.) to which the ject occasionally applied to this wire. The magnifiers

concave speculum, for reflecting light on opaque objects, in the slider E are mounted in a wheel case, which perPlate, is fixed. At S is a hole and slit for receiving either the baps prevents its being in the way so much as the long CCCXLI.

nippers L (fig. 31.) or the fish-pan I, when these are slider E before described.--This contrivance is repre-
used, the slider-holder must be removed. T, a hole to sented at X, fig. 12.
receive the pin of the convex lens M.

4. Martin's New Universal Compound Microscope.-
To use this microscope : Take it out of the box. This instrument was originally constructed by Mr B.
Screw the body into the round end of the upper part Martin, and intended to comprise all the uses and ad-
of the arm CD. Place the brass sliders, which con- vantages of the single, compound, opaque, and aquatic
tain the magnifiers, into the dove-tailed slit which is microscopes. The following is a description of it.
on the under side of the aforesaid arin, as seen at E, Fig. 13. is a representation of the instrument pla- Plate
and slide it forwards until the magnifier you mean ced up for use. ABCD is the body of the micro-CCCXXXII.
to use is under the centre of the body: opposite to scope : which consists of four parts, viz. AB the eye-

fig. 13. each magnifier in this slit there is a notch, and in piece, or that containing the eye-glasses, and is screwthe dove-tailed part of the arm CD there is a spring, ed into C, which is a moveable or sliding tube on the which falls into the above-mentioned potch, and tbus top ; this inner tube contains the body-glass screwed makes each magnifier coincide with the centre of the into its lower part. D is the exterior tube or case, hody. Pass the ivory slider you intend to use between in which the other slides up and down in an easy and the upper plates of the slider-holder KL, and then steady manner. This motion of the tube C is useful reflect as strong a light as you can on the subject by to increase and decrease the magnifying power of the means of one of the mirrors ; after this, adjust the ob- body-glass when thought necessary, as before mentionject to the focus of the magnifier and your eye, by ed." E is a pipe or snout screwed on to the body of the turning the milled screw M, the motion of which raises microscope D, and at its lower part, over the several and depresses the stage NIS. The degree of light magnifying lenses bereafter described. FGHI is the necessary for each object, and the accuracy required in square stem of the microscope, upon which the stage the adjustment of the Jenses to their proper focal di- R moves in an horizontal position, upwards or downstance from the object, will be easily attained by a little ward, by means of the fine rack work of teeth and pinion. practice.

KL is a strong solid joint and pillar, by which the po-
When opaque objects are to be examined, remove sition of the instrument is readily altered from a verti-
the slider-holder, and place the object on a flat glass, cal one to an oblique or to a perfectly horizontal one as

or fix it to the nippers L, the pin of these fit into the may be required : it is thus well adapted to the ease of
hole on the stage ; screw the concave speculum R the observer either sitting or standing ; and as it is very
into the arm Q (Hig, 31.), and then pass the pin of this often convenient to view objects by direct unreflected
arm through the socket D (fig. 12.); the light is now light, when the square stem FI is placed in a horizon-

to be reflected from the concave mirror to the silver spe- tal position for this purpose, the mirror T is then to be
culum, and from this down on the object. No exact taken off in order to prevent the obstruction of the
rule can be given for reflecting the light on the object; rays. M is a circular piece of brass, serving as a base
we must therefore refer the reader to the mother of all to the pillar. NOP, the tripod or foot by which the
aptness, practice. The speculum must be moved lower whole body of the microscope is steadily supported; it ·
or higher, to suit the focus of the different magnifiers folds up when packed into the case. W is, a brass
and the nature of the object.

frame, that contains the condensing lens, and acts in
The foregoing directions apply equally to the using conjunction with the large concave and plane mirrors
of this instrument as a single microscope ; with this dil. below at T; the reflected rays from which, either of
ference only, that the body AB is then removed, and the common light or of that of a candle or lamp, it
exactly over the magnifiers.
the eye is applied to the upper surface of the arm CD, agreeably modifies, and makes steady in the field of

This microscope is sometimes made with the follow- The partieulars of the apparatus to this microscope
ing alterations, which are supposed to make it still are as follow : Q is a circular brass box, containing six
more convenient and useful. The arm CD that car- magnifiers or object lenses, numbered 1, 2, 3, 4, 5, 6 g
ries the body and magnifiers is made both to turn on the digits of which appear severally through a small

pin, and to slide backwards and forwards in a socket round bole in the upper plate of it. To the upper side
at C; so that, instead of moving the objects below on is fixed a small circle of brass, by which it is connected
the stage, and disturbing them, the magnifiers are more with; and screwed into, the round end of the arm
conveniently broaght over any part of the objects as, abcd; which is a long piece of brass, and moves through
desined. The condensing glass is made larger, and either by teeth or pinion, or not, as may be desired, in
siides upon the square bar CF quite distinct from the ef; which is a socket on the upper part of the pillar,
stage, like the mirrors below; and it is thereby made and admits, with a motion both easy and steady, the







at a.

Fig. 14.


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Micro- brass arm. R is a fixed stage, upon which the objects ing of a concave glass with a plane ono screwed over Micre

to be viewed are to be placed : it is firmly fastened to it; by means of which a bug, louse, flea, &c. may be seope.
the square pillar, which is moved by the rack-work. secured and viewed alive. It is to be placed on either
In the middle is a large circular hole, for receiving of the stages R (fig. 13.), or Nos. (fig. 14.).
concave glasses, with fluids, &c.; it has also a sliding N° 13. is the fish pan. In the long concave body
spring frame to fasten down slips of glass or other things: a b, a fish may be so confined by the ribband c, that
at abo are three small sockets or holes, intended to the transparent tail may be in part over the slit or hole
receive several parts of the apparatus. S is the refrac- In this state, it is placed on the stage R, with
tor, or illuminating lens, for converging the sun's rays the pin d in the hole c of the stage, and moves free-
upon opaque objects laid upon the stage R. To this ly and horizontally for viewing the circulation of the
purpose it moves on a semicircle upon a long shank g, blood, &c.
in a spring socket h, in the arm i ; this arm moving N° 14. is the slider-bolder that is placed on the stage
every way by a stout pin k in the socket a of the stage. R: it receives the sliders and tubes when filled with
In this manner it is easily adjusted to any position of the transparent objects, to be viewed either by the com-
sun, candle, &c.-.T, the reflecting-glass frame, con- pound or single microscope.
taining a concave and plane speculum, which is moved No 15. represents the ivory slider, to hold the objects
upon the square pillar by the hand. The use of it is to between the talcs as usual.
illuminate all transparent objects that are applied to the N° 16. is a useful auxiliary slider framed in brass.
stage above.

In this slider small concave glasses are cemented; and
Fig. 14. N° 1. is an auxiliary moveable stage ; which a slip of plane glass slides over them; by which any
by means of a pin k is placed in the hole a of the stage small living object, as mites, &c. may be confined with-
R, and can be moved in a horizontal direction over out injury, and deliberately viewed.
the whole field of the stage. In this stage, there are 17. represents a set of glass tubes, three in num-
three circular holes with shouldered bottoms; a large ber, one within another; they are useful for small tad-
one in the middle, and on each side a small one, poles, water netts, cels, &c. when the circulation of
for the reception of the three following necessary arti- the blood is to be viewed. There is a small hole at
cles : No 2. a watch-glass to be placed in the large hole, one end of each tube, that serves to admit the air; for
to hold Avids containing animalcules, &c.; a circu- then they are filled with water, the other end is stop-
lar piece of ivory, No 3. one side of which is black, the ped with a cork.
other white, to support opaque objects of different con- N° 18. is a small ivory box, containing spare talcs
trasted colours ; and circular plane and concave glasses, and wires, to supply the sliders with occasionally.
N° 4. forextemporaneoustransparent objects. The same N° 19. a brass cell or button, containing a very small
use is made of the other small hole as of the large one, lens, properly set between two small plates of brass,
only in a lesser degree, to receive small concave glasses, that it may be brought very near to the object when
plates, &c.

viewed therewith as a single microscope. This magni-
N° so is the silvered speculum, called a liberkhun, fier is screwed into the same hole as the wheel of six
which makes the single opaque microscope, by being magnifiers Q are (fig. 13.).
screwed to the slider abc d (fig. 13.) in room of the box N° 20. is a lens, adapted to view and examine ob-
of lenses Q, and the body AE above it. The chief jects, by magnifying them sufficiently, so as to be able
use of this is to view very small objects strongly illu- to apply them to the microscope for inspection : on this
minated near the compounded focus of the mirror account it is called the explorator.
T (fig. 13.). N° 6. is the forceps or pliers, for holding The preceding are the chief articles of the appara-
such kind of objects, and by which they can be ap- tuş : which, on account of their being somewhat dif-
plied very readily to the focus of the lens in the li- ferent from what is applied to other microscopes, we
berkbun. They have a motion all ways by means of have been thus particular in describing. In using
the spring socket a, the joint b, and the shank c: the microscope, and while viewing objects by either
they are placed in the socket c. of the fixed stage R the single or compound instrument, the focal distances
(fig. 13.). ? No.7. is a small piece of ivory, to be of the magnifiers are made perfectly exact by turn-
placed upon the pointed end of the pliers : it is black ing of the pinion at the nut w, in one way or the
upon one side, and white upon the other, to receive other, very gently in the teeth of the rack-work at
opaque objects.

X (fig. 13.).
N° 8. is a liberk hun of a larger size than that first It is necessary that the centres of the object-lenses
mentioned, with a hole in its centre: this is screwed. or magnifiers, the stage, and the mirrors at bot-
into No 9. the hole a of a brass ring, fastened to a long tom, should all be in a right line irr the axis of the
wire b; which moves up and dowa in the spring soc-microscope, when opaque objects are to be viewed,
ket b.of the stage R, in which it also moves sideways; that are placed upon the ivory piece N° 7. or the for-
and thụs, with the body AE above, forms an aquatic -ceps No 6. and all other such sort of objects which are
-compound microscope for showing all sorts of objects in placed in the centre of the stage R, or slider-holder
water and other fluids placed under it in the watch-glass N° 14: But when aquatic or living objects, which re-
N9 2. on the stage.

quire a great space to move in, are to be viewed, then
No 11. is a cone, with a proper aperture a to exclude the horizontal motion at ef (fig. 13.) is made use of,
superfluous light, that would disturb a critical observa, and the view may be extended laterally over the whole
tion of a curious object; it is placed on the under side of the diameter of the object or field of view; and
of the fixed stage R.

by putting the arm abcd forward or backward in N° 12. is what is usually called a bug-box, consist- its socket ef, the view is extended in the coptrary



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Micro scope.



direction equally well; and in this manner the whole two screws (11). N° 6. (fig. 16.) represents a move- Micro of the objects may be viewed without the least disturb- able stage, which is placed in the spring socket m.

It scope. contains a concave glass, for the reception of animal

Fig. 16.
As the brass arms a bed may be brought to the cules in Auids ; and has the advantage of bringing any

height of three or four inches above the stage R; so, part into view by moving the handle at n.

If living by means of the rack-work motion of the stage, a and moving objects are required to be shown, the must lens of a greater focal distance than the greatest in be confined in the concave, by putting a glass cover, the wheel Q may be occasionally applied in place of N° 7. upon the stage ; and then a small spider, a louse, the wheel, and thereby the larger kind of objects be a flea, bug, &c. may be seen, and the motion or cirviewed; the instrument becoming, in this case, what is culation of the blood, &c. observed with surprising dicalled a megalascope.

stinctness. In viewing moving living objects, or even fixed ones, To view the circulation of the blood in the most when nice motions are requisite, a rack-work and pi- eminent degree, it must be done by placing small frogs, nion is often applied to the arm abcd: the arm is tadpoles, water-newts, fishes, &c. in a tube as reprecut out with teeth ; and the pinion, as shown at Y, is sented No 8. (fig. 17.); which tube is placed in the Fig. 17. applied to work it. This acts but in one direction ; holes o in the opposite sides of the case a b, fig. 15. in and, in order to produce an equally necessary motion the lower part --No 9. (fig. 16.) is a pair of pincers perpendicular to this, rack-work and pinion is applied or pliers d, for liolding any object; the other end of tangent-wise to the stage, which is then jointed. the steel wire is pointed to receive a piece of ivory b,

with one end black, and the other white, on which you What has been related above respects the construc- stick objects of different hue : . this also, when used, is tion of those denominated parlour microscopes, in con placed in the spring socket m. tradistinction to those which are portable: their di- To use this instrument as a compound opaque, you mensions, however, have been considerably reduced by screw off the body part a b, and screw to it the bandle opticians, in order to render them fit for the pocket; po (fig. 16.); by this means you may hold the microand as they are for the most part constructed on nearly scope in a horizontal position, as shown in the figure. the same principles as those wbich bave been already The silver dish or speculum (which is contained in the described, what has been said will sufliciently instruct bottom or base k, fig. 15.), is then screwed on at b. our readers in using any pocket microscope whatever. N° 9. is placed in the spring soeket m, and adjusted Only it may be observed, that in those reduced instru- backward and forward in m, till the reflected light from ments, both the field of view and the magnifying the speculum falls in a. proper manner on the opaque power are proportionably diminished.

object. Either of the four magnifiers, 2, 3, 4, 5, may be

used, and brought to a proper focus, as before describWe shall conclude the account of this sort of mi- ed by the tooth and pinion e (fig. 15.). If you take eroscope with descriptions of a very portable pocket off the opaque apparatus, and apply the stage No 1. (fig. apparatus of microscopic instruments, and of a new mi- 16.) with an ivory slider, and at the end b screw in either croscopic pocket telescope, both invented by the late of the two lenses, No 10. (which are distinguished by Mr B. Martin, and since made by most instrument- the name of illuminators), the microscope being held up makers in London.

to the light (and properly adjusted), the whole field of The former is represented at. fig. 15. It consists view will be strongly illuminated, and present a most: of two parts, viz. the body a b, and the pedestal i k, pleasing appearance of any transparent object. These which is joined by a screw at the part between b and two convex lenses are of diferent focuses, and are to be i. It consists of three cylindric tubes, viz. (1.) the used singly or together ; N° 2. being the greatest magniexterior tube, or case, ab; ( 2.) a middle tube cb; fier, will require the object to be strongly illuminated, and (3.) the interior tube f g. The middle tube and of course both the lenses must be used together. cd is the adjueter; and is connected with the outer By candle-light, this method of viewing transparent olitube by the rack-work of teeth and pinion, as shown jects will prove very entertaining ; by screwing the at e : by which means it is moved up and down at handle r into the part s of No 10. it becomes a delightpleasure through the smallest space, and carries with ful hand megalascope for viewing flowers, fossils, shells, it the internal tube fg. The interior tube f g receives &c,; and each lens, as before mentioned, baving a on its lower part at the several capsules or boxes 2, different focus, produces two magnifying powers used 3, 4, 5, (fig. 16.) which contain the object lenses or singly, and when combined a third.

The manner of using this instrument as a single mi. The method of using this compound microscope in croscope (like Wilson's) is represented in fig. 17. where the perpendicular position, is as follows: The stage the button or magnifier at each is to be screwed off, and No 1. is put within the exterior tube at b. Un- the circular piece N° 11. is screwed in its place. This der the springs are applied the four ivory sliders, piece has a spring socket made to receive the slider-hclwhich contain a variety of transparent objects; then

der No 12.

13. is a circular piece of brass, with a. move the interior tube f g up and down with the hand, long shank and spring, and is introduced through the till you discern the object in the slider, and there let outside tube ab at to N° 2, 3, 4, 5, are screwed occait rest. After this, turn the pinion at'e very tenderly sionally in the centre of this piece, and used as single one way or the other, till you obtain a perfect view lenses with ivory sliders, &c. N° 14. contains a lens of of the transparent objects properly. illuminated, from a great magnifying power, for viewing very minute oba mirror contained in the pedestal or stand ik, sus- jects : to render this instrument the most complete single pended upon, and moveable about, the points of opaque microscope, you have only to screw into N° 13. Vol. XIV. Part I.




Fig. 15.

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taken away

Micm. the silver speculum No 15. which has a small lens set in and the mirror B placed therein, and the wheel with Micra. its centre.

The slider-holder No 12. is taken out of transparent objects. C (fig. 20.) represents the wheel scope. No 11, and the pincers or nippers db, being detached with transparent objects, and D the wheel with opaque from the other part of No 9. are passed through the objects. They are both made of ivory; and turn long spring socket N° 11. and ready to receive any round upon a centre brass pin slit upon the top, which opaque body in the pincers, or on the black and white fits upon the edge of the tube ; which tube is then to piece of ivory. To the large screw of N° 13. are applied be pushed up into the telescope tube, so that its lower the two lenses N° 10. which make it the completest end may rest upon the upper edge of the wheel acmegalascope that can be desired.

cording to its view at a, fig. 18. The handle r contains the four ivory sliders with In viewing the objects, the second brass tube of the objects.

telescope must be pushed down, till its milled edge at The shagreen case which contains this universal mi- top falls upon that of the exterior tube ; taking care croscope and its apparatus, is six inches long, three that the circular hole is duly placed to the exterior one. inches wide, tıro inches deep; and weighs together 16 These circular holes are not seen in fig. 18. being supounces. “Thus (says Mr Martin) so small, so light, posed in the opposite side, where the wheel is fixed. so portable, and yet so universally complete, is this The adjustment for the focus is now only necessary; pocket microscopic apparatus, that you find nothing which is obtained by pushing downwards or upwards material in the large three-pillared microscope, the the proper tube, till the object appear quite distinct. opaque microscope, Wilson's single microscope, and In viewing transparent objects

, the instrument may be the aquatic microscope, all, together, which you bave used in two positions ; one vertical, when the light is to not in this ; besides some very considerable advantages be reflected upon the object by the mirror; the other, in regard to the field of view, &c. which they bave by looking up directly against the light of a candle, not (A).”

common light, &c.; in which case the mirror must be This inventive artist having contrived a construc

In viewing opaque objects, the mirror is tion of the compound microscope so small as to admit of not used; but as much common light as possible must be being packed in a common walking cane, thought next admitted through the circular holes in the sides of the of introducing the same instrument into the inside of tubes. what be called his Pocket Three-brass drawer Achro- There is a spare hole in the transparent wheel, and matic Telescope. The same eye glasses that serve the also one in the opaque, to receive any occasional object purpose of a telescope, answer as the compound magni-' that is to be viewed. Any sort of object whatsoever fier, for viewing transparent and opaque objects in a may be viewed, by only pushing up the microscope microscope.

tube into its exterior, and bringing the first eye-tube Fig. 18, 19, 20, represent the telescope separated to its focal distance from the object. by unscrewing it at m, in order that the whole of The brass tubes are so contrived, that they stop the necessary parts in use may be exhibited. Fig. 19. when drawn out to the full length : so that by represents the exterior tube, which is of mahogany, applying one hand to the outside tube, and the and its rinus of brass. It is detached from the rest of other to the end of the smallest tube, the telescope at the telescope, as not making any part of the micro- one pull may be drawn out; then any of the tubes scope. The brass cover k l, that shuts up the object- (that next to the eye is best) may be pushed in graglass of the telescope, is also the box which contains dually, till the most distinct view of the object be obthe two-wheel object frames, and a small plain reflect

tained. ing mirror.

The tubes all slide through short brass spring tubes,
In fig. 20. A is the cover taken off

, by unscrew

may be unscrewed from the ends of the ing the top part : The mirror B is taken out; and al- sliding tubes by means of the milled edges which proso, by unscrewing the bottom part, the two circular ject above the tubes, taken from each other, and the wheels, with the objects sbown in C and D.

springs set clear if required. Fig. 18. is a representation of the three internal brass sliding tubes of the telescope, which form the

III. Of Solar Microscopes. microscopic part. The tubes are to be drawn out as shown in this figure; then, at the lower end of the This instrument, in its principle, is composed of a large tube in the inside, is to be pulled out a short tube, a looking-glass or mirror, a convex lens, and tube b c, that serves as a kind of stage to bold the Wilson's single microscope before described. The sun's wheels, with objects

, and support the reflecting mirror. rays being reflected through the tube by means of the This tube is to be partly drawn out, and turned so mirror upon the object, the image or picture of that the circular hole that is pierced in it may coin- the object is thrown distinctly and beautifully upon ·cide with a similar hole that is cut in the exterior tube. a screen of white paper or a white linen sheet, placed This tube is represented as drawn out in the figure ; at a proper distance to receive the same; and may be




any of which

(A) Notwithstanding the properties that have been ascribed to the above instrument, and the praises bestowed upon it by some, which induced us to admit so minute a description, we must apprise our readers, that it has been omitted in Mr Adams's enumeration; and upon inquiry we learn, that it has fallen into neglect among the most judicious opticians, being found too imperfect to serve the purposes of science, and too complicated for the use of persons who seek only entertainment.






Micro- magnified to a size not to be conceived by those light upon the screen before you apply the micro-
scope. who have not seen it: for the farther the screen is re- scope, is a certain proof that your mirror is adjusted

moved, the larger will the object appear; insomuch, right, that proof must not always be expected : for the
that a louse may thus be magnified to the length of sun is so low in winter, that if it shine in a direct line
five or six feet, or even a great deal more; though it against the window, it cannot then afford a spot of
is more distinct when not enlarged to above half that light exactly round; but if it be on either side, a

round spot may be obtained, even in December. As
The different forms in which the Solar Microscope is soon as this appears, screw the tube D into the brass
CCCXL. constructed, are as follow.

collar provided for it in the middle of your wood-work, fig. 21.

I. The old construction is represented in fig. 21. A taking care not to alter your looking-glass: then is a square wooden frame, through which pass two screwing the magnifier you choose to employ to the long screws assisted by a couple of nuts 1, 1. By these end of your microscope in the usual manner, take away it is fastened firmly to a window shutter, wherein a hole the lens at the other end thereof, and place a slider, is made for its reception ; the two nuts being let into containing the objects to be examined, between the the shutter, and made fast thereto. A circular hole thin brass plates, as in the other ways of using the miis made in the middle of this frame to receive the piece croscope. of wood B, of a circular figure ; whose edge, that Things being thus prepared, screw the body of projects a little beyond the frame, composes a shallow the microscope over the small end E of the brass tube groove 2, wherein runs a catgut 3 ; which, by twist- F; which slip over the small end E of the tube D, ing round, and then crossing over a brass pulley 4, and pull out the said tube D less or more as your

ob(the handle whereof s, passes through the frame), ject is capable of enduring the sun's heat. Dead obaffords an easy motion for turning round the circular jects may be brought within about an inch of the piece of wood B, with all the parts affixed to it. C focus of the convex lens 5; but the distance must is a brass tube, which, screwing into the middle of the be shortened for living creatures, or they will soon be

, circular piece of_wood, becomes a case for the unco- killed. vered brass tube D to be drawn backwards or forwards If the light fall not exactly right, you may casily, in. E is a smaller tube, of about one inch in length, by a gentle motion of the jointed wire and pulley, dicemented to the end of the larger tube D. F is rect it through the axis of the microscopic lens. The another brass tube, naade to slide over the above de- short tube F, to which the microscope is screwed, scribed tube E; and to the end of this the microscope renders it easy, hy sliding it backwards or forwards on must be screwed, when we come to use it. 5. A con- the otber tube E, to bring the objects to their focal res lens, whose focus is about 12 inches, designed to distance ; which will be known by the sharpness and collect the sun's rays, and throw them more strongly clearness of their appearance: they may also be turn; upon the object. G is a looking-glass of an oblong ed round by the same means without being in the least figure, set in a wooden frame, fastened by hinges in disordered. the circular piece of wood B, and turning about The magnifiers most useful in the solar microscope therewith by means of the above-mentioned catgut. are in general, the fourth, fifth, or sixth. The screen H is a jointed wire, partly brass and partly iron ; on which the representations of the objects are thrown, the brass part whereof 6, which is flat, being fastened is usually composed of a sheet of the largest elephant to the mirror, and the iron part 7, which is round, paper, strained on a frame which slides up or down, or passing through the wooden frame, enable the observer, turns about at pleasure on a round wooden pillar, after by putting it backwards or forwards, to elevate or de- the manner of some fire screens. Larger screens may press the mirror according to the sun's altitude. There also be made of several sheets of the same paper pasted is a brass ring at the end of the jointed wire 8, where- together on cloth, and let down from the ceiling with a by to manage it with the greater ease. The extremi- roller like a large map. ties of the catgut are fastened to a brass pin, by turn- “ This microscope (says Mr Baker) is the most ening of which it may be braced up, if at any time it beu tertaining of any; and perhaps the most capable of comes too slack.

making discoveries in objects that are not too opaque :. When this microscope is employed, the room must as it shows them much larger than can be done any

as dark as possible ; for on the darkness other way. There are also several conveniences atof the room, and the brightness of the sunshine, de- tending it, which no other microscope can have : for pend the sharpness and perfection of your image. the weakest eyes may use it without the least straining Then putting the looking-glass G through the hole in or fatigue : numbers of people together may view any your window shutter, fasten the square frame A to the object at the same time ; and by pointing to the partichuiter by its two serews and nuts 1, 1. This done, cular parts thereof, and discoursing on what lies before

your looking-glass to the elevation and situation them, may be able better to understand one another,
of the sun, by means of the jointed wire H, together and more likely to find out the truth, than in other
with the catgut and pulley, 3, 4.

For the first of microscopes, where they must peep one after another,
these raising or lowering the glass, and the other in and perhaps see the object neither in the same light nor
clining it to either side, there results a twofold mo- in the same position. Those also, who have no skill in
tion, which may easily be so managed as to bring the drawing, may, by this contrivance, easily sketch out.
glass to a right position, that is, to make it reflect the the exact figure of any object they have a mind to pre-
rays directly through the lens 5, upon paper

serve a picture of; since they need only fasten a paper
screen, and form thereon a spot of light exactly round. on the screen, and trace it out thereon either with a
But though the obtaining a perfect circular spot of pen or pencil, as it appears before them. It is worth

be rendered




B 2


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