An Account of the latest Modifications in the Structure of the Amician Catadioptric Microscope, with full and particular directions for managing and observing with it. By J, Cuthbert. Communicated by the Author.

DR. GORING, in his account of the improvements which have been made in England on the Reflecting Microscope of Professor Amici, has given directions for using the instrument, but such as I find by experience to be inadequate to enable observers, not greatly habituated to the use of microscopes, to manage it in an effective manner. The following description and instructions are intended, with the help of the wood engravings, to supply the place of a vivá voce lecture upon the instrument itself, and are adapted to the standard of the meanest capacity.

When the instrument is removed from the box, nothing more is required than to reverse the legs, and draw back the slide on the small tube containing the reflectors.

Fig. 1,

Shews the instrument ready for

use.

(a.) The tube containing the reflectors.

(b.) The slide which covers the aperture, to preserve the reflectors when not in use. The tube can be unscrewed to substitute the other reflectors, which differ in magnifying power.

(c.) The eye-tube, which can be drawn out to apply others, which also vary the power.

(d.) Shews the milling of an internal tube, which may be partly drawn out, thereby lengthening the body, and thus giving a further increase of power, or intermediate powers between those produced by the eye-tubes.

(e.) The slider holder for supporting the objects; it may be detached from the stage at pleasure.

(f, g.) Two adjusting screws, by which the slider holder can be moved in cross directions for the purpose of bringing any part of the object to the centre of the field of view.

(h.) The screw by which the object is adjusted to the focus.

(i.) The milled head which clamps the screw apparatus to the bar of the instrument, after roughly adjusting the focus, by moving it up and down on the bar: the correct adjustment is effected by the screw h.

(j.) The illuminator, which has a concave and a plane surface, to be used at discretion.

(k.) The pillar, composed of two tubes; the internal one can be drawn out to raise the instrument, either for the convenience of the observer, or to regulate the light from the lamp, which should also have a similar adjustment.

(1.) The screw for tightening the cleft-socket, by which means the body of the instrument with its apparatus can be kept in any required position, the variety of motions given by means of the cleft socket 1, the joint m, and the sliding pillar k, leaves nothing further to be desired, either in point of utility or convenience.

Fig. 2,

(a.) Shews the position of the small condensing lens placed on the neck of the body; it is capable of being moved in any direction, to condense the rays from a lamp, &c., to illuminate an opaque object.

Fig.3,

Shews the instrument in its best position, when direct daylight is intercepted for shewing transparent objects without the illuminator; and Fig. 4 for direct lamplight, &c.

Fig. 3.

Fig. 5.

The universal forceps, which fixes on in place of the stage (as represented at Figs. 6 and 12);. it will be found very convenient, affording great facility of presenting all parts of the object under examination to the action of the reflectors.

272

Mr. Cuthbert on the

Fig. 6.

wera,weiv snildo as al x9 Tot tпemuto 197liz edido art of Iso sivad of do odt and beneath the mirror, for the purpose of view-siz ing crystallization of salts, &c., which are placed labia yas to on a piece of talc, held in the forceps over the aperture, by which arrangement the reflectors are preserved from being injured by the steam

Shews the body turned round vertically in its spring socket b, until the aperture in the tube containing the reflectors is directly upwards

10

of the salt entering the aperture. The light is O
then to be directed or condensed by the illumi-
natorj, through the fluid.

Fig. 7,

Is a piece to connect the forceps with the traversing work of the stage, used in lieu of the slider holder, e, Fig. 1, (which is liberated by being turned a quarter round,) the piece is then capable of being moved by the two adjusting screws ƒ and g. In some cases itu may be found convenient to remove the stage wholly from the

socket of the adjusting screw apparatus, and apply the forceps in its place. In that case the connecting piece, Fig. 7, is not applied.

Fig. 8,

4

Is a moveable object-carrier, which slips between the orde bars of the sliderholder, e, Fig. 1, and is used for holding concave glasses, or a box to contain living aquatic objects, for animalculæ, &c.; also a black surface, for to opaque objects.

Is the live, or aquatic box, the glasses of which are capable of being oqs placed at various distances, to suit the particular kind of object.git

Fig. 10,

lenses, Is a section of the eye-tube, shewing the position of the lenses, builybol

Is a section

Fig. 11,

do quis of the tube and reflectors, shewing their position in situ, a, the aperture through which the rays pass from the object to the plane reflector 4, which is placed at an angle of forty-five degrees, and directs the rays towards the concave reflector c, from which they are transmitted through the body and eye-tube to the eye of the ob

Is an oblique view, shewing the position of the instrument for examining opaque objects; a, the silver cup with its aperture centrical to that of the tube b; c, the object to be viewed placed directly opposite the aperture of the said tube, so as to prevent any side light from entering; d, is the large condensing lens which slides upon the bar, instead of

the double reflector, and is to be placed about four inches from the silver cup a. The candle, or lamp, must also be about the same dise tance from the lens.

Fig. 13,

Is the silver cup, shewing the spring clamps a, a, which attach it a to the tube of the reflectors.

ti

Fig. 14,

Shews one of the cork opaque object-holders placed on a pin havom ing an an object stuck on each side. They are preserved in a box with a n cork bottom to fix them into. The small-sized holders are for the high os odd eso tedn

powers.

Fig. 15,

ra;

Is a black ground to be used when a small opaque object is held in the forceps unattached to a cork holder, and requiring to be turned round to exhibit its different parts: it is connected to d to the socket of the tightening screw, Fig. 1, i, by the pin a the black disk b, also serves to prevent false light from enter ing the aperture. The wire which holds it can be adjusted to the requisite distance by sliding it up and down in the arm which supports it Disks of different sizes are adapted to the different, illuminating cupsde!

Fig. 16,

Is an arm to carry single lenses; it slips on the neck of the body in the place of the tube of reflectors, thereby making most convenient single microscope, if required.

The most convenient method of proceeding to examine objects is as follows:-After setting up the instrument, and drawing back the slide on the tube of reflectors, turn the illus minator towards the light, and at such an angle, that the rays bos.299129b 25 ut femonds bothmans es vedt

-do grit to 979 9 oct

may be thrown up to the small aperture of the tube, containing the reflectors, when the field of view is perfectly illuminated, an even, round, and bright disk of light will be seen in the body of the instrument, or the illuminator may be removed, and the body of the instrument turned round, to procure the simple and unreflected light, which, in most cases, will be found the best method of procedure. (See Figs. 3 and 4.) The slider containing the object to be examined may then be introduced between the bars and spring plate of the slider-holders, remembering to place that side of the slide on which the brass ring is not seen, next to the tube of reflectors. The object may then be adjusted to the focus in the following manner:—

First slack the screw (i, Fig. 1), then slide the whole of the screw apparatus up or down, till the object is nearly in the focus; then tighten the screw (i) and perfect the adjustment, by turning the milled head of the screw (h). It is proper to remark, that, as the brightness and ease of vision must necessarily decrease with the increase of magnifying power, it should be so arranged as to suit the particular kind of object under examination, using no more amplification than is absolutely necessary. A low power is best suited to make out the general character of an object in the first instance; it may then be increased for investigating its more minute parts.

The low powers may be used for opaque objects, without the condensing lens, if the daylight is bright, or by merely bringing the lamp towards the side of the tube, containing the reflectors. When the higher powers are used, the small condensing lens, as shewn in Fig. 2, must be made use of, placing the light the same distance from the lens as the lens is from the object, viz., about an inch and a half.

The most powerful mode of illuminating for high powers is obtained by the use of the condensing cups and large lens, the arrangement of which is shown by Fig. 12. This method shows objects in a brilliant light, with scarcely any shadow, and answers well for the generality of opaque objects.

Some require oblique lights to produce a shadow, such as the fine lines on the scales of the diamond beetle, which can scarcely be seen by a direct light, and, in such cases, the small