Chapter L: M N is a guide for the eye, in order to direct it in the axis of the (1)

lenses; it consists of two brass tubes, one sliding within the other, and a vertical flat piece, at the top of which is the hole for the eye. The outer tube is seen at M N, the vertical piece is represented at L M. The inner tube may be pulled out, or pushed in, to adjust it to the focus of the glasses. The vertical piece may be raised or depressed, that the hole, through which the object is to be viewed, may coincide with the center of the field of view; it is fixed by a milled screw at M, which could not be shewn in this figure.

At N is a dove-tailed piece of brass, made to receive the dove-tail at the end of the tubes M N, by which it is affixed to the wooden box A B C D E. The tubes M N may be removed from this box occasionally, for the convenience of packing it up in a less compass.

O P a small tube on which the magnifiers are screwed.

O one of the magnifiers; it is screwed into the end of a tube, which slides within the tube P; the tube P may be unscrewed occasionally from the wooden body.

Q R S T V X a long square bar, which passes through the sockets Y Z, and carries the stage or frame that holds the objects; this bar may be moved backward or forward, in order to adjust it to the focus, by means of the pinion which is at a.

b e is a handle furnished with an universal joint, for more conveniently turning the pinion. When the handle is removed, the nut, Fig. 2, may be used in its stead.

d e is a brass bar, to support the curved piece K I, and keep the body A B firm and steady.

f g h i is the stage for opake objects; it fits upon the bar Q R S T by means of the socket h i, and is brought nearer to, or removed farther from the magnifying lens, by turning the pinion a; the objects are placed in the front side of the stage, which cannot be seen in this figure, between four small brass plates; the edges of two of these are seen at k l. The two upper pieces of brass are moveable; they are fixed to a plate, which is acted on by a spiral spring that presses them down, and confines the slider with the objects; this plate, and the two upper pieces of brass, are lifted up by the small nut m.

At the lower part of the stage, there is a glass semiglobe n, which is designed to receive the light from the lamp, Fig. 3, and to collect and convey it to the concave mirror o, from whence it is to be reflected on the object.

The upper part, f g r S, of the opake stage takes out, that the stage for transparent objects may be inserted in its place.

Fig. 4. represents the stage for transparent objects; the two legs 5 and 6, fit into the under part r S of the stage for opake objects; 7 is the part which confines or holds the sliders, and through which they are to be moved; 9 and 10 a brass tube, which contains the lenses for condensing the light, and throwing it upon the object; there is a second tube within that, marked 9 and 10, which may be placed at different distances from the object by the pin 11.

When this stage is used as a single microscope, without any reference to the lucernal, the magnifiers or object lenses are to be screwed into the hole 12, and to be adjusted to a proper focus by the nut 13.

N. B. At the end A B of the wooden body there is a slider, which is represented as partly drawn out at A; when quite taken out, three grooves will be perceived, one of which contains a board that forms the end of the box, the next contains a frame with a greyed glass; the third, or that farthest from the end A B, two large convex lenses.

OF THE LAMP.

Fig. 3, represents one of Argand’s lamps, which is the most suitable for microscopic purposes, on account of the clearness, the intensity, and the steadiness of the light. The following method of managing it, with other observations, is copied from an account given by Mr. Parker, with those he sells.

The principle on which the lamp acts, consists in disposing the wick in thin parts, so that the air may come into contact with all the burning fuel, by which means, together with an increase of the current of air occasioned by rarefaction in the glass tube, the whole of the fuel is converted into flame.

The wicks are circular, and, the more readily to regulate the quantity of light, are fixed on a brass collar with a wire handle, by means of which they are raised or depressed at pleasure.

To fix the wick on, a wood mandril is contrived, which is tapered at one end, and has a groove turned at the other.

The wick has a selvage at one end, which is to be put foremost on the mandril, and moved up to the groove; then putting the groove into the collar of the wick-holder, the wick is easily pushed forward upon it.

The wick-holder and wick being put quite down in their place, the spare part of the wick should, while dry, be set alight, and suffered to burn to the edge of the tubes; this will leave it more even than by cutting, and, being black by burning, will be much easier lighted: for this reason, the black should never be intirely cut off.

The lamp should be filled an hour or two before it is wanted, that the cotton may imbibe the oil, and draw the better.

The lamps which have a reservoir and valve, need no other direction for filling, than to do it with a proper trimming pot, carefully observing when they are full; then pulling up the valve by the point, the reservoir being turned by the other hand, may be replaced without spilling a drop.

Those lamps which fill in the front like a bird-fountain, must be reclined on the back to fill, and this should be done gently, that the oil in the burner may return into the body when so placed and filled; if, by being too full, any oil appear above the guard, only move the lamp a little, and the oil will disappear; the lamp may then be placed erect, and the oil will flow to its proper level.

The oil must be of the spermaceti kind, commonly called chamber oil, which may generally be distinguished by its paleness, transparency, and inoffensive scent; all those oils which are of a red and brown colour, and of an offensive smell, should be carefully avoided, as their glutinous parts clog the lamp, and the impurities in such oil not being inflammable, will accumulate and remain in the form of a crust on the wick. Seal oil is nearly as pale and sweet as chamber oil, but being of a heavy sluggish quality, is not proper for lamps with fine wicks.

Whenever bad oil has been used, on changing it, the wick must also be changed, because, after having imbibed the coarse particles in its capillary tubes, it will not draw up the fine oil.

To obtain the greatest degree of light, the wick should be trimmed exactly even, the flame will then be completely equal.

There will be a great advantage in keeping the lamp clean, especially the burner and air tubes; the neglect of cleanliness in lamps is too common: a candlestick is generally cleaned every time it is used, so should a lamp; and if a candlestick is not to be objected to, because it does not give light after the candle is exhausted, so a lamp should not be thought ill of, if it does not give light when it wants oil or cotton; but this last has often happened, because the deficiency is less visible.

The glass tubes are best cleaned with a piece of wash leather.

If a fountain lamp be left partly filled with oil, it may be liable to overflow; this happens by the contraction of the air when cold, and its expansion by the warmth of a room, the rays of the sun, or the heat of the lamp when re-lighted: this accident may be effectually prevented by keeping the reservoir filled, the oil not being subject to expansion like air. On this account, those with a common reservoir are best adapted for microscopic purposes.

TO EXAMINE OPAKE OBJECTS WITH THE LUCERNAL MICROSCOPE.

The microscope is represented as mounted, and entirely ready for this purpose, in Fig. 1. Plate III.

To render the use of this instrument easy, it is usually packed with as many of the parts together as possible; it occupies on this account rather more room, but is much less embarrassing to the observer, who has only three parts to put on after it is taken out of its box, namely, the guide for the eye, the stage, and the tube with its magnifier.

But to be more particular, take out the wooden slide A, then lift out the cover and the grey glass from their respective grooves under the slide A.

Put the end N of the guide for the eye L M N into its place, so that it may stand in the position which is represented in this figure.

Place the socket, which is at the bottom of the opake stage, on the bar Q X T, so that the concave mirror o may be next the end D E of the wooden body.

Screw the tubes P O into the end D E. The magnifier you intend to use is to be screwed on the end o of these tubes.

The handle G b, or milled nut, Fig. 2, must be placed on the square end of the pinion a.

Place the lamp lighted before the glass lump n, and the object you intend to examine between the spring plates of the stage, and the instrument is ready for use.

In all microscopes, there are two circumstances which must be particularly attended to; the modification of the light, or the proper quantity to illuminate the object; secondly, the adjustment of the instrument to the focus of the glasses and the eye of the observer. In the use of the lucernal microscope there is a third circumstance, which is the regulation of the guide of the eye, each of which I shall consider by itself.

1. To throw the light upon the object. The flame of the lamp is to be placed rather below the center of the glass semiglobe n, and as near it as possible; the concave mirror o must be so inclined and turned, as to receive the light from the semiglobe; and reflect it thence upon the object; the best situation of the concave mirror, and the flame of the lamp, depends on a combination of circumstances, which a little practice will best point out.

2. To regulate the guide for the eye, or to place the center of the eye piece L, so that it may coincide with the focal point of the lenses, and the axis of vision. Lengthen and shorten the tubes M N by drawing out or pushing in the inner tube, and raising or depressing the eye-piece M L, till you find the large lens, which is placed at the end A B of the wooden body, filled by an uniform field of light, without any prismatic colours round the edge; for, till this piece be properly fixed, the circle of light will be very small, and only occupy a part of the lens; the eye must be kept at the center of the eye-piece L, during the whole of the operation; which may be rendered somewhat easier to the observer, on the first use of the instrument, if he hold a piece of white paper parallel to the large lenses, removing it from or bringing it nearer to them, till he finds the place where a lucid circle, which he will perceive on the paper, is brightest and most distinct, then to fix the center of the eye-piece to coincide with that spot; after which a very small adjustment will set it perfectly right.

3. To adjust the lenses to their focal distance. This is effected by turning the pinion a, the eye being at the same time at the eye-piece L. I often place the grey glass before the large lenses, while I am regulating the guide for the eye, and adjusting for the focal distance.

If the observer, in the process of his examination of an object, advance rapidly from a shallow to a deep magnifier, he will save himself some labour by pulling out the internal tube at O.

The upper part f g r s of the stage, is to be raised or lowered occasionally, in order to make the center of the object coincide with the center of the lens at O.

To delineate objects, the grey or rough ground glass must be placed before the large lenses; the picture of the object will be formed on this glass, and the outline may be accurately taken, by going over the picture with a pencil.

The opake part may be used in the day-time without a lamp, provided the large lenses at A B be screened from the light.

TO USE THE LUCERNAL MICROSCOPE IN THE EXAMINATION OF TRANSPARENT OBJECTS.

The microscope is to remain as before: the upper part f g r s of the opake stage must be removed, and the stage for transparent objects, represented at Fig. 4, put in its place; the end, Fig. 9 and 10, to be next the lamp.

Place the rough glass in its groove at the end A B, and the objects in the slider-holder at the front of the stage; then transmit as strong a light as you are able on the object, which you will easily do, by raising or lowering the lamp.

The object will be beautifully depicted on the rough glass: it must be regulated to the focus of the magnifier, by turning the pinion a.

The object may be viewed either with or without the guide for the eye; a single observer will see an object to the greatest advantage by using this guide, which is to be adjusted as we have described, page 73. If two or three wish to examine the object at the same time, the guide for the eye must be laid aside.

Take the large lens out of the groove, and receive the image on the rough glass; in this case the guide for the eye is of no use: if the rough glass be taken away, the image of the object may be represented on a paper screen.[29]

[29] A tin cover is sometimes made to go over the glass chimney of the
lamp, Fig. 3, with only a small square aperture in front, sufficient
to suffer the rays to pass into the microscope: this, by excluding all
extraneous rays, adds in many cases most materially to the effect,
particularly by day, and when objects are to be represented on the
rough glass or screen only. EDIT.

Take out the rough glass, replace the large lenses, and use the guide for the eye; attend to the foregoing directions, and adjust the object to its proper focus. You will then see the object in a blaze of light almost too great for the eye, a circumstance that will be found very useful in the examination of particular objects; the edges of the object in this mode will be somewhat coloured, but as it is only used in this full light for occasional purposes, it has been thought better to leave this small imperfection, than by remedying it, to sacrifice greater advantages; the more so, as this fault is easily corrected, and a new and interesting view of the object is obtained, by turning the instrument out of the direct rays of light, and permitting them to pass through only in an oblique direction, by which the upper surface is in some degree illuminated, and the object is seen partly as opake, partly as transparent. It has been already observed, that the transparent objects might be placed between the slider-holders kl of the stage for opake objects, and then be examined as if opake.

Some transparent objects appear to the greatest advantage when the lens at 9 and 10 is taken away; as, by giving too great a quantity of light, it renders the edges less sharp.

The variety of views which may be taken of every object, by means of the improved lucernal microscope, will be found to be of great use to an accurate observer: it will give him an opportunity of correcting or confirming his discoveries, and investigating those parts in one mode, which are invisible in another.

TO TRANSMIT THE IMAGE OF TRANSPARENT OBJECTS ON A SCREEN, AS BY THE SOLAR MICROSCOPE.

It has been long a microscopical desideratum, to have an instrument by which the image of transparent objects might be shewn on a screen, as by the common solar microscope; and this not only because the sun is so uncertain in this climate, and the use of the solar microscope requires confinement in the finest part of the day, when time seldom hangs heavy on the rational mind, but as it also affords an increase of pleasure, by displaying its wonders to several persons at the same instant, without the least fatigue to the eye.

This purpose is now effectually answered, by affixing the transparent stage, Fig. 4, of the lucernal to a lanthorn containing one of Argand’s lamps. The lamp is placed within the lanthorn, and the end 9, 10 of the transparent stage is screwed into a female screw, which is rivetted in the sliding part of the front of the lanthorn; the magnifying lenses are to be screwed into the hole represented at 12; they are adjusted by turning the milled nut. The quantity of light is to be regulated, by raising and lowering the sliding plate, or the lamp. N. B. This part, with its lanthorn and lamp, may be had separate from the lucernal microscope.[30]

[30] This effect by the lanthorn and lamp is subject to much
limitation in the field of view, or circle of light thrown upon the
screen. A circle of not more than from 12 to about 15 inches can ever
be obtained with any tolerable strength of light, to shew the most
transparent sort of objects that can be found, such as the scale of a
sole fish, a fly’s wing, &c. The great difference between the light of
the sun and a lamp is a natural obstacle to great performances in this
way, and renders them far short of the effects of the solar
microscope. The exhibition, however, is considerable, and much
deserving of the notice of any observer disposed to this sort of
apparatus. Probably, subsequent experiments may yet produce more light
on this instrument. The best sort of apparatus for this purpose
hitherto made, I shall describe in a following section. EDIT.

APPARATUS WHICH USUALLY ACCOMPANIES THE IMPROVED LUCERNAL MICROSCOPE.

The stage, Fig. 1, f g h i, for opake objects, with its glass semiglobe, and concave mirror, which is moveable upon the bar Q R S T, and set readily to any distance by the screw at a. The glasses o and n are also moveable upon the bar for regulating and adjusting the light upon the object.

The stage, Fig. 4, for transparent objects, which fits on the upper part P S of the foregoing stage. When this is to be applied occasionally to a lanthorn for shewing transparent objects on a screen, &c. it is made of a much larger diameter, to admit of the illuminating lenses at 9, 10, and 11, of greater power of condensing the rays from the lamp.

The sliding tube O P, to which the magnifiers are to be affixed; one end of this is to be screwed on the end B of the wooden body; the magnifier in use is to be screwed to the other end on the inner tube. This tube slides inwards or outwards; it is first used to set the magnifier at nearly the right distance from the object, before the exact adjustment for the focus is made, by turning the pinion at a with Hook’s joint and handle b e.

Eight magnifying lenses in brass cells, Fig. 5. Plate III. these are so constructed that any two of them may be combined together, and thus produce a very great variety of magnifying powers. The cells unscrew to admit of the glasses being cleaned.

A fish-pan, such as is represented at Fig. 6, whereon a small fish may be fastened in order to view the circulation of its blood; its tail is to be spread across the oblong hole at the smallest end, and tied fast by means of the attached ribbon. The knob on its back is to be put through a slit hole on the brass piece, No. 5, of Fig. 4. The tail of the fish is to be brought then immediately before the magnifier.

A steel wire, Fig. 7, with a pair of nippers at one end, and a steel point at the other; the wire slides backwards or forwards, in a spring tube which is affixed to a joint at the bottom, on which is a pin to fit the hole in the leg, No. 6, Fig. 4. This is used to confine small objects.

A slider of brass, Fig. 8, containing a flat glass slider and a brass slider, into which are fitted some small concave glasses. It is for confining small living objects, and when used is placed between the two plates, No. 7, Fig. 4.

A pair of forceps, Fig. 9, by which any occasional small object may be conveniently taken up.

Six large ivory sliders, with transparent objects placed between two plates of talc, and confined by brass rings, and six small ditto with ditto. Fig. 10. The larger ones usually contain a set of Custance’s fine vegetable cuttings.

Fourteen wood sliders, containing on each four opake objects, and two spare sliders for occasional objects; all fitted to the cheeks kl of the stage. Fig. 11.

Some capillary tubes, Fig. 12, to receive small fish, and for viewing small animalcula. They are to be placed between the two plates of the stage No. 7, Fig. 4.

A small ivory double box, containing spare plates of talc and brass rings, for replacing any in the small ivory sliders, when necessary.

A single lens mounted in a tortoiseshell case, to examine minute objects previous to their being applied to the sliders.

Opake objects are easily put on the spare sliders by a wetted wafer; and, for good security, gum water may be added.

For the prices of the lucernal, as well as all the other sorts of microscopes, see the list annexed to these Essays.

A DESCRIPTION OF THE SEVERAL IMPROVEMENTS MADE UPON MR. ADAMS’S LUCERNAL MICROSCOPE. BY THE EDITOR.

The lucernal microscope being unquestionably the only instrument for exhibiting all sorts of opake objects under a brilliant and magnified appearance, was, as formerly constructed by the late Mr. G. Adams, attended with some inconveniences and imperfections. Upon a proper inquiry into various improvements, and from some observations made by myself, I can recommend, as a complete instrument, one with the following emendations, being, in my opinion, the best of any hitherto made known.

The lucernal microscope, when placed up for use, as represented in Fig. 1. Plate III. is of some considerable length. When the eye at L is viewing the image of the object upon the glasses, the objects themselves in the sliders placed at kl at the stage, are without the reach of the hand; so that the indispensible change of the parts of an object, or of one object to another, can only be obtained by the observer’s moving himself from the object to the eye-piece, and vice versa. This adjustment, therefore, proves uncertain and troublesome. The application of rack-work motion to the stage has been contrived and applied to the lucernal microscope by Mr. W. Jones, of Holborn, accompanied with Hooke’s joint and handle, and a lever rod; so that, without altering his position, the observer may change both the horizontal and vertical position of the sliders, and thereby readily investigate all the variety of the objects, and their parts, and with the same exactness as by other microscopes.

For persons who may not wish to be at the expense of the lucernal, as formerly mounted by Mr. Adams, Mr. Jones has altered the manner of its support; which, as well as the other particulars, and the method of using it, may be understood from the following description.

Plate IX. Fig. 3, is a representation of the instrument as placed up for use. AA, the top of a mahogany chest, about two feet long, thirteen inches and an half high, and eight inches broad, which serves both as a case to contain the instrument, and to support and preserve it steady when in use. A groove is cut in the top of the box, and another in the inside at the bottom, in both of which the base of the instrument is made to slide. When the instrument is placed inside, a long slip of mahogany slides in at the top, to secure the groove, and make the top perfect. Thus the instrument may be most readily slid out of its case, and then into the groove at top for use, and in much less time than by the brass frame and jointed stand adopted by Mr. Adams. Fig. 3 B, is the stage for the objects, with the condensing lens _a_, and concave mirror _b_, the same as in Mr. Adams’s. C, the brass slider case for opake objects, with a rack cut into its lower edge, and which is turned by a pinion. To this pinion is applied an handle, D, with Hooke’s universal joint; this contrivance gives a certain horizontal motion to the objects while viewing. The stage at C is also made to slide vertically, and a lever-rod or handle, E, to apply through the top, to bring the objects to a just height. Hence, by applying the left hand to the handle, E, and the right to the rod D, the adjustment or the changing of the objects, while under exhibition on the large lenses at F, is produced in the most convenient and accurate manner, and the observer has no occasion, for one slider, to shift from his seat or position.

Rack-work might be applied to the vertical motion, but it is not essentially necessary; for when once the center of the slider is observed, there requires very little change from that position for the complete exhibition of the objects. The whole of the stage, with the lense and mirror, is fixed to a brass dove-tailed slider at G, which slides in another brass piece fixed to the wooden slider or base of the instrument. A long brass rod, H, with an adjusting screw at its end, passes through the two brass pillars, K, K, to the stage at _f_, upon which it acts; and according as it is turned to the right or left hand while examining the objects, moves the objects nearer to or farther from the magnifiers screwed on at L, and produces the just distance for rendering the appearance of the objects the most distinct and brilliant upon the glasses at F.

The management of the light from the lamp, through the lens, _a_, and from the concave mirror, _b_, to the objects, is exactly the same as before directed by Mr. Adams. For the exhibiting of transparent objects, the stage, C, is to be slid away, and the body, Fig. 4, applied in its place, in that position, with the large lens outwards next the lamp. The slider with the objects passes through at _a_, and the focus for the different magnifiers is adjusted by turning the long rod, D, to the right or left, as with the opake objects. In this case the lamp is to be raised to the center of the body of the microscope, or even with the magnifiers at L. The image of the objects may also, as in Mr. Adams’s, be best received on the rough glass placed at F, for the simple reflected light through the body will sometimes be so strong, as to irritate the eye; the operator must, therefore, both modify that from the lamp, and place the roughed glass to his own ease and pleasure. The guide for the eye, N, in this instance is not necessary. Care being taken that the roughed glass at F be kept in as dark a situation as possible, there will be a certainty of a clear and well-defined view of the object.

A tin chimney placed over the glass of the lamp about ten inches long, with a suitable aperture to admit the light to pass through it to the glasses, is of material service; it excludes all superfluous light from the eye of the observer, keeps the room sufficiently darkened, and enables the observer to view his object with the proper brilliancy. As a pleasing relief to the eye, the interposition of a small piece of blue or green glass at the sight hole, N, Mr. Jones has sometimes found necessary, but it gives rather a false teint to the colour of the objects.

In the year 1789 the same artist applied a brass screw pillar and arm to the top of the box at O, on which is occasionally slid the condensing lens, _a_. The lamp being then applied at the side of the box at O, instead of the end, and the lens, _a_, moved to such a distance as to give the strongest possible light upon the opake objects at C; they were found to be more strongly illuminated by this simple refracted light than by the refracted and reflected light before used. Light is always somewhat diminished by reflection, although condensed; therefore, as it is sometimes best to view the objects from oblique reflected light, and sometimes from direct refracted, he constructs the apparatus so as to give the operator the means of easily using either. The dotted lines, O P, shew the manner that the glass semiglobe, _a_, is occasionally applied to refract or converge directly the light from the lamp to the objects on the stage.

It is scarcely necessary to observe to the reader, the propriety of all the glasses of the apparatus being perfectly clean before the observations; for if, after being laid aside some time, or by dust, &c. they should appear soiled, it will be necessary to wipe them previously with a piece of soft shammy leather usually sent in the box for that purpose, or a clean soft cloth. The two large lenses at F, Fig. 3, may be readily separated by turning aside the two brass screws that act upon a brass ring.

From the various ingenious admirers of this sort of instrument, many improvements and alterations have been suggested; among several that have been communicated, those by the two following gentlemen appear to me the most deserving of notice, and which I shall leave to the reader’s judgment and experience.

The Rev. John Prince, LL. D. now of Salem, Massachuset’s States, North America, a valuable correspondent and friend of our late author, transmitted to him an alteration in the construction; and of which I here insert the brief account, in nearly the words given by Mr. Adams.

Dr. Prince applies a strong joint similar to that of a telescope at about the middle of the center part of the pyramidical box, and a sort of adjusting screw at the large end. The joint is nearly in the center of gravity, so that a very small motion is sufficient to bring any object less than an inch in diameter into the field of view. This motion is effected by two screws at right angles to each other; one screw raising or levelling the body, the other moving it sidewise, the screw at the same time forming a double joint to accommodate the parts to the movement.[31]

[31] A figure of this, with an explanation, as recommended by Mr. John
Hill, Wells, in Norfolk, may be seen in the Gentleman’s Magazine, Vol.
LXVI. 2d part, page 897. In this particular, as well as in the
deviation from the parallel position of the glasses to the surfaces of
the objects, I think the construction not so simple and perfect, as
that by rack-work and pinion applied by Mr. Jones. Probably, Dr.
Prince had not, at the time of his contriving the joint-work to the
box, seen or heard of the other method. His subsequent contrivances
shew real ingenuity; and to the inquisitive in this instrument, will
afford much useful entertainment and advantage.

To secure the image formed upon the rough glass more completely from the light, at times essentially necessary, there is a pyramidical mahogany box, of the same size, to pack, when not used, in the body of the microscope; when in use, the broad end of this screen box is to be slid into the groove, from which the exterior cover at the end has been taken. This method is peculiarly useful in the day-time; as, by screening the large lenses from the light, it may even then be used with satisfaction.

One of the large lenses may occasionally be placed on the outer edge of the screen box, the other lens being taken out; the view on the rough glass is by these means magnified, and appears to greater advantage. But, besides the grey glass used in the former construction, there is a second in this, placed farther within the body, about half way; and, when the large lens is in the screen box, objects appear better in this than in the former way. It has a still greater effect upon those who are unacquainted with the nature of lenses, as it makes them judge the distance and magnitude much greater than they really are, and is therefore more pleasing than the grey glass in front. Only one grey glass can be used at a time; both being removed when opake objects are viewed.

The stage, F, Fig. 5, is considerably different from that at C, Fig. 3; it is judged more convenient and commodious than the other, and serves, with a small alteration, for both transparent and opake objects. A truncated cone can also be here applied for cutting off superfluous rays of light occasionally.

The method of illuminating the objects is also different. The mode now adopted answers better for opake and transparent objects, throws a stronger light, and is more convenient in application. It consists of two lenses, 1 and 2, Fig. 5; the larger one is to be placed at the end of the bar next the lamp. The smaller one to be adjusted so as to give a strong light. A third is also added, to be used occasionally with opake objects; it is to be applied close to the large lens. Experience will shew when it is to be used, or not. By moving the bar, G, on which these lenses are placed round the stage pillar, M, you bring it so much fronting the stage as effectually to enlighten opake objects by means of the lamp. The light thus afforded is received directly, and none lost by reflection. The objects are fixed on circular wheels of wood, see Fig. 7, the brass centers of which, are fitted to the hole, _b_, of the stage, Fig. 5; and about this center they are to be turned by the hand for the changing of the objects.

As some objects, such as sections of wood, are seen to advantage both as transparent and opake, a frame containing a plane and a concave mirror is added to this instrument, serving two purposes: by bringing the bar to the front of the stage, removing the large lens, and putting the mirror in its place, the object may be viewed either way, without moving from the seat, by turning the instrument a little round. This experience will discover. The light of the sun may be thrown by the plane mirror on the condensing lens, so as to produce a strong full field of light on the grey glass. This has a grand effect when the large lens is at the end of the screen box, and could not be applied in this manner in former constructions. It becomes also an opake solar microscope, by turning the bar round to enlighten opake objects.

By bringing the concave mirror to a focus that will burn objects, a set of very curious and entertaining experiments may be made and exhibited on the grey glass. The object for combustion should be put in the nippers, and a piece of slate tied as a ground on the stage. The ebullition of a piece of alum viewed in this manner is very beautiful; the bubbles, as they rise and pass off rapidly, appear tinged with all the colours of the rainbow.

There are large-sized magnifiers for the purpose of throwing transparent objects on a screen, in imitation of the solar microscope. By removing the large lenses in front and the grey glass, and placing the black tin cylinder represented in the drawing by dotted marks, over the lamp, they may be shewn in that manner to several persons; thus, this instrument in a great degree supersedes the use of a lanthorn. The image may be contracted occasionally by one of the large lenses.

The following improvement consists in the manner of applying the lamp, by Mr. Hill. By attaching it to the instrument, it renders the light more permanent and steady, and reduces considerably the bulk as well as the trouble of this appendage, and is to be preferred when the lamp is not wanted separately for other uses or experiments.

H, a brass support to the arm, G, for sustaining the weight of the lamp; it turns round with the bar on the pillar, M. At about I is a brass cap soldered to the above support, and which slips over the slider carrying the larger lens, 2. At K, is a strong joint connected with the said cap, and by which an horizontal motion of the cap is given, when an oblique light is required. To the end of this the lamp is fixed, and in such a manner as to admit of its being easily slid upwards or downwards in a perpendicular direction, to procure the just height of the flame. L is a square brass rod to be occasionally screwed into the reservoir of the lamp, for supporting the tin cylinder screen, when transparent objects are to be represented on a screen in a darkened room.

The transparent microscope, part of the lucernal, is sometimes adapted to a large japanned tin lanthorn, such as represented at Fig. 6. A brass female screw is soldered to the front of the lanthorn, which has a motion upwards or downwards, fitted to the male screw of the transparent microscope. A tall chimney is placed at the top of the lanthorn to conduct the heated air from an Argand’s lamp withinside. The transparent objects in the sliders are magnified by the lenses screwed on at _a_, and shewn on the screen A; this screen may be about three feet square, of white paper, the objects on which, if represented in a field larger than twelve or eighteen inches, will not be sufficiently vivid.

Mr. Jones has found that a large square glass, from twelve to sixteen inches in the side, rough ground on one of its surfaces, exhibits the objects the best of any other contrivance; answers tolerably well for opake objects, and gives the artist the means of tracing their figure most correctly on its surface. Such sort of objects he fixes upon slips of glass for that purpose, or applies them to a pair of nippers shewn at _b_, sent with the microscope. A concave silver speculum screws on at _c_, before the magnifiers, which reflects upon the objects the light that issues from the lamp through the body of the microscope. The least dimensions of the lanthorn are about ten inches square, and fourteen inches high.

This microscope and lanthorn, when made as a separate apparatus from the lucernal, is called the LANTHORN MICROSCOPE. Its effect is considerably short of what is produced by the solar microscope, and not equal to what is much wished for in this manner of magnifying minute objects; see note, page 77.

Partly from the improvements just described, Mr. Jones is now constructing a lucernal microscope that he conceives will be the most simple and perfect yet made. It could not be completed in time to be described in this work; but its improvement and advantages will be quite evident to any reader who has attended to the description which I have just given.

DESCRIPTION OF CUFF’S DOUBLE-CONSTRUCTED MICROSCOPE, REPRESENTED AT Fig. 1. Plate VII. A.[32]

[32] The compound or double microscope is in more general use than any
other sort. Besides its being less expensive than the lucernal or
complete solar, it is found commodious and portable in the observer’s
apartment, when only a confined degree of microscopical pursuit is
intended, and that chiefly for a few hours amusement; it may be used
both by day and night. In the most improved of this kind the objects
appear magnified in a field of view from about 12 to 15 inches in
diameter. It is better adapted to transparent than to opake objects,
yet the latter may often be viewed to great advantage by the
assistance of the sun’s rays or the light of a candle condensed on
them. The intelligent reader, by attending to the accounts of the
different microscopes described in this work, will be enabled to
select that best adapted to the kind of objects he wishes to explore,
and the manner in which he is desirous of having them exhibited. EDIT.

This instrument was first described by Mr. Baker, and recommended by him. It was also described by my father in the fourth edition of his Micrographia Illustrata, page xix.

A B C represents the body of this microscope; it contains an eye-glass at A, a large lens at B, and a magnifier which is screwed on at C, one of which is represented at Q.

The body of the microscope is supported by the arm D E, from which it may be removed at pleasure.

The arm D E is fixed on the sliding bar F, and may be raised or depressed to any height within its limits.

The main pillar a b is fixed in the box b e, and by means of the brass foot d is screwed to the mahogany pedestal X Y, in which is a drawer containing all the apparatus.

O, a milled-headed screw, to tighten the bar F when the adjusting screw c g is used.

p q is the stage or plate which carries the objects; it has a hole at the center n.

G, a concave mirror, that may be turned in any direction, to reflect the light of the candle, or the sky, upon the object.

A LIST OF THE APPARATUS TO CUFF’S DOUBLE-CONSTRUCTED MICROSCOPE.[33]

[33] This microscope is made oftentimes with a joint at the bottom of
the main pillar at _e_, to admit placing the instrument into any
oblique situation, and connected to the bottom of a mahogany chest; on
which account, it is by some of the instrument makers called the Chest
Compound Microscope. EDIT.

H, a convex lens, to collect the rays of light from the sun or a candle, and condense them on the object, or to magnify a flower or other large object placed upon the stage.

L, a cylindrical tube, open at each side, with a concave silver speculum screwed to the lower end h.

P, the slider-holder; it consists of a cylindrical tube, in which an inner tube is forced upwards by a spiral spring, it is used to receive an ivory slider K, which is to be slid between the plates h and i. The cylinder P fits the hole n in the stage: the hollow part at k is designed to receive a glass tube N.

R is a brass cone, to be put under the bottom of the cylinder P, to intercept occasionally some of the rays of light.

S, a box containing a concave and a flat glass, between which a small living insect may be confined; it is to be placed over the hole n.

T, a flat glass to lay any occasional object upon; there is also a concave one u, for fluids.

O, a long steel wire, with a small pair of pliers at one end, and a point at the other, designed to stick or hold objects; it slips backwards and forwards in the short tube o; the pin p fits into an hole m, in the stage for that purpose.

W, a little round ivory box, to hold a supply of talc and rings for the sliders.

Z, a hair brush, to wipe any dust off the glasses, or to take up by the other end a drop of any liquid.

V, a small ivory cylinder, that fits on the pointed end of the steel wire O; it is designed for opake objects. Light-coloured ones are to be stuck upon the dark side, and vice versa.

Y, a common magnifying glass for any occasional purpose.

M, a fish-pan whereon to fasten a small fish, to view the circulation of the blood: the tail is to be spread across the oblong hole at the small end k, and tied fast by means of a ribband fixed thereto; the knob l is to be put through the slit made in the stage, and the tail may be brought under the magnifier.

X is a wire to clean the glass tubes by.

TO USE THIS MICROSCOPE.

Screw the magnifier you intend to use to the end C of the body, place the slider-holder P in the hole n, and the ivory slider K with the object, between the plates _h i_ of the slider-holder; set the upper edge of the bar D E to coincide with the division which corresponds to the magnifier you have in use, and tighten it by the milled nut O; now reflect a proper quantity of light upon the object, by means of the concave mirror G, and regulate the body exactly to the eye and the focus of the glasses by the adjusting screw _c g_, at the same time you are viewing the object.

To view opake objects, take away the slider-holder P, and place the object on a flat glass u, under the center of the body, or on one end of the jointed nippers o. Then screw the silver concave speculum to the end of the cylinder L, and slide this cylinder on the lower part of the body, so that the upper edge thereof may coincide with the line which has the same mark with the magnifier that is then used; reflect the light from the concave mirror G to the silver speculum, from which it will be again reflected on the object. The glasses are to be adjusted to their focal distance as before directed.

THE DESCRIPTION AND USE OF JONES’S IMPROVED COMPOUND OR DOUBLE MICROSCOPES, REPRESENTED IN Fig. 1 AND 2. Plate IV. BY THE EDITOR.

The chief imperfections of Cuff’s microscope, as well as of others formerly made, are, their construction rendering them only compound microscopes, the body of the instrument having but a fixed position over the object, and the smallness of the field of view by the old construction of the glasses in the body. To obviate these defects, as well as for the application of material improvements, the late Messrs. Martin and Adams, and the present Messrs. W. and S. Jones, have constructed this kind of microscope in various ways. Two microscopes by the latter artists, which I am now going to describe, appear to me to be the best of any hitherto invented.

Fig. 1 is a representation of the second best sort of compound microscopes. The improvements, though few in number, are essential to the use thereof. The field of view is considerably larger than in the former microscope. The stage and the mirrors are both moveable, so that their respective distances may be easily varied. The magnifiers may be moved about over the object. There is also a condensing glass, for increasing the density of the light, when it is reflected by the mirror from a candle or lamp. It is furnished with two mirrors, one plane and the other concave, and may likewise be used as a complete single microscope.

A B, Fig. 1. represents the body of the microscope, containing a double eye glass, and a body glass; it is here shewn as screwed to the arm C D, from whence it may be occasionally removed, either for the convenience of packing, or when the instrument is to be used as a single microscope.

The eye glasses and the body glasses are contained in a tube which fits into the exterior tube A B; by pulling out a little this tube, when the microscope is in use, the magnifying power of each lens is increased.

The body A B of the microscope is supported by the arm C D; this arm is moveable in a square socket cut in the head that is connected to the main pillar E F, which is screwed firmly to the mahogany pedestal G H; there is a drawer to this pedestal, which holds the apparatus. This arm may be slid backwards and forwards in its socket, carrying the magnifiers and the body of glasses, and also turned horizontally quite round upon the pillar, giving a general motion all over the object on the stage below; which is a material improvement and advantage of this microscope over a similar one described in the former edition of this work, as any unavoidable motion of the living object to be viewed may be followed, by the observer’s hand moving the arm C D as the object changes its place.

N I S is the plate or stage which carries the slider-holder K, this stage is moved up or down the pillar E F, by turning the milled nut M; this nut is fixed to a pinion, that works in a toothed rack cut on one side of the pillar. By means of this pinion the stage may be gradually raised or depressed, and the object adjusted to the focus of the different lenses.

K is the slider-holder, which fits into a hole that is in the middle of the stage N I S; it is used to confine and guide either the motion of the sliders which contain the objects, or the glass tubes that are designed to confine small fishes, for viewing the circulation of the blood. The sliders and tubes are to be passed between the two upper plates.

L is a brass tube, in the upper part of which is fixed the condensing lens before spoken of; it screws into the wire arm a, which is placed in the hole I of the stage, with the glass underneath, and may be set at different distances from the object, according to its distance from the mirror or the candle.

O is the frame which holds the two reflecting mirrors, one of which is plane, the other concave. These mirrors may be moved in various directions, in order to reflect the light properly, by means of the pivots on which they move, in the semicircle Q, and the motion of the semicircle itself on the pin R; the concave mirror generally answers best in the day-time; the plane mirror combines better with the condensing lens in L, and a lamp or candle at night.

At S is a hole and slit for receiving either the nippers _b_, or the fish-pan _c_; when these are used, the slider-holder K must be removed.

T, a hole to receive the pin of the convex lens and illuminator _d_.

There are six magnifying lenses contained in a brass wheel screwed in a circular brass box P; this wheel is moveable about its center with the finger, and stops by a click when the magnifiers are each centrally under the body A B above, or the hole in the arm C D. They are marked from No. 1, to 6, and the proper number shewn in a small opening made in the side of the brass box. This wheel P screws into the arm C D, and may occasionally be taken off to admit of the silver speculum, or a single magnifier, hereafter to be described.