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.