THEM.
In the preceding chapter I have endeavoured to give a comprehensive view
of the theory of the microscope, and the principles on which the
wonderful effects of this instrument depend. I shall now proceed to
describe the various instruments themselves, their apparatus, and the
most easy and ready mode of applying them to use; selecting for
description those that, from some peculiar advantage in their
construction, or from the reputation of the authors who have recommended
and used them, are in most general use. What is said of these will, I
hope, be sufficient to enable the reader to manage any other kind that
may fall in his way.
DESCRIPTION OF ADAMS’S IMPROVED AND UNIVERSAL LUCERNAL MICROSCOPE. Fig.
1. Plate III.
This microscope was originally thought of, and in part executed by my
father; I have, however, so improved and altered it, both in
construction and form, as to render it altogether a different
instrument. The approbation it has received from the most experienced
microscopic observers, as well as the great demand I have had for them,
has fully repaid my pains and expenses, in bringing it to its present
state of perfection.
As the far greater part of the objects which surround us are opake, and
very few sufficiently transparent to be examined by the common
microscopes, an instrument that could be readily applied to the
examination of opake objects, has always been a desideratum. Even in the
examination of transparent objects, many of the fine and more curious
portions are lost, and drowned as it were in the light which must be
transmitted through them; while different parts of the same object
appear only as dark lines or spots, because they are so opake, as not to
permit any light to pass through them. These difficulties, as well as
many more, are obviated in the lucernal microscope; by which opake
objects of various sizes may be seen with ease and distinctness; the
beautiful colours with which most of them are adorned, are rendered more
brilliant, without in the least changing their natural teints. The
concave and convex parts of an object retain also their proper form.
The facility with which all opake objects are applied to this instrument
is another considerable advantage, and almost peculiar to itself; as the
texture and configuration of the more tender parts are often hurt by
previous preparation, every object may be examined by this instrument,
first as opake, and afterwards, if the texture will admit of it, as
transparent.
The lucernal microscope does not in the least fatigue the eye; the
object appears like nature itself, giving ease to the sight, and
pleasure to the mind: there is also in the use of this instrument, no
occasion to shut that eye which is not directed to the object.
A further advantage peculiar to this microscope is, that by it the
outlines of every object may be taken, even by those who are not
accustomed to draw; while those who can draw well, will receive great
assistance, and execute their work with more accuracy, and in less time
than they would otherwise have been able to have performed it in. Most
of the designs for this work were taken with the lucernal microscope;
and I hope the accuracy with which they are executed, will be deemed a
sufficient testimony in favour of the instrument. In this point of view
it will, I think, be found of great use to the anatomist, the botanist,
the entomologist, &c. as it will enable them not only to investigate the
object of their researches, but to convey to others accurate
delineations of the subject they wish to describe.
By the addition of a tin lanthorn, transparent objects may be shewn on a
screen, as by the solar microscope.
Transparent objects may be examined with this instrument in three or
four different modes; from a blaze of light almost too great for the eye
to bear, to that which is perfectly easy to it.
When this instrument is fitted up in the best way, it is generally
accompanied with a small double and single microscope.
Fig. 1. Plate III. represents the IMPROVED LUCERNAL MICROSCOPE, mounted
to view opake objects; A B C D E is a large mahogany pyramidical box,
about fourteen inches long, and six inches square at its larger end,
which forms the body of the microscope; it is supported firmly on the
brass pillar F G, by means of the socket H, and the curved piece I K.
L M N is a guide for the eye, in order to direct it in the axis of the
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.