aperture 40 mm. wide, which can be wholly or partially covered by two sliding plates.

A special Brücke magnifier (with variable power) screws on the arm M. The arm has also a spring-tube into which a smaller mirror

FIG. 14.

can be inserted. This is for illuminating opaque objects, and receives its light from the larger mirror below. The focus of both mirrors is so regulated that with high powers the theoretically possible maximum of illumination can always be nearly attained. For very weak illumination there is on one side a plate of opal glass. "The mirror has the great advantage over ordinary illuminating lenses that the field of view is always somewhat faintly and evenly illu

Hc

minated, which extraordinarily facilitates the visibility of many natural objects which have not sharp outlines." The upper mirror can be placed in any position with regard to the axis of the lower, and can besides, for special objects, be put in the spring-tube of the lower mirror.

The Brücke lens consists of two achromatic objective lenses and a concave eye-lens. The objective lenses can be moved apart or brought nearer to one another by turning the ring R. In the same way the eye-lens can be placed at various distances from the objective by pushing the tube N up or down. This tube is so sprung in the inner fastening that by a somewhat firm pressing together of the two knobs k, the friction of the two tubes is lessened and an easy and smooth movement is obtained. For very low powers the lower objective lens can be removed. By this combination and also two stronger eye-pieces all gradations of power, in the given limits, can be obtained. The extent of the field of view is in inverse ratio to the power within the limits of 65 to 7 mm.

FIG. 15.

For convenient drawing a camera lucida is attached, which like Zeiss's allows the drawing surface to be inclined about 22° to the table. On turning the ring R, or on moving the tube to alter the power the camera always remains in the same position with regard to the ocular and the drawing surface, which is claimed to be "an advantage not to be undervalued, and not considered in many instruments."

In order to use the instrument for dissecting there are hand-rests, made to be easily removed. They consist of two hollow boxes (fig. 14) about 2/3 the height of the stage. They are attached by the button-headed screws c to the foot of the instrument, being inserted in the holes C1 and C2 B (fig. 13) and the hinged tops can be set at different inclinations by the support and rack.

Zeiss's Micrometer Eye-piece.-This (fig. 15) is noticeable for the manner in which the micrometer disk is inserted. The eye-piece divides a little below the middle of its length, and has an additional piece between the upper and lower portions to which they are screwed. In this the micrometer disk is placed. The eye-lens is also in a sliding tube for adjustment to different sights.

Bulloch's Objective Attachment.-Mr. W. H. Bulloch has devised the objective-attachment shown in figs. 16 and 17. A is the nose-piece adapter to screw on the Microscope, and B is the ring, provided with three wedge-shaped studs, to be screwed on the objective. Three slots are cut in the body of the lower cylinder of the nose-piece A, and three similar slots in the inward projecting rim of a rotating collar. When the two sets of slots correspond, the ring B, with the objective attached, can be slid into the nose-piece, and then the studs are locked firmly by a slight turn of the rotating collar, which causes its projecting rim to slide over the outer halves of the studs. By reason of the wedge form given to the studs, the collar can be made to press down upon them with more or less force. The objective cannot be removed from the nose-piece until the rotating collar is turned back to the normal position, releasing the studs.

With this device both hands must be used either in attaching or removing the objective, and no provision is made to insure accuracy of centering. In the apparatus from which the above description was

B

made the objective had a lateral play at the shoulder of about 1/50 in. when the collar was secured with moderate force. Such loose fitting would be found very inconvenient in the registration of the positions of small objects with high powers. Altogether, we cannot but think that the apparatus is more complicated than is at all necessary. Whilst it has the studs of Nelson's form it lacks the simplicity of the turn of the objective with the same hand that holds it, and whilst it has the rotating collar of the Watson-Matthews form (amply sufficient to hold the objective) it has the additional complication of studs in place of a simple conical fitting.

Abbe's Camera Lucida.*-G. Kohl gives the annexed fig., 18, of

what he terms "Boecker's new drawing apparatus after Dippel," but which is in reality Professor Abbe's Camera Lucida.†

*Bot. Centralbl., xvi. (1883) pp. 385-6 (1 fig.).
+ See this Journal, iii. (1883) p. 278.

The novelty consists in the introduction of the tinted glass plates rrr in the path of the rays from the mirror. Also the upper part of the apparatus (mirror p, its arm a, the glasses rrr, and the plate o 8) is movable on the pivot q upon the lower plate, which forms part of the tube h fixed to the eye-piece by k.

Millar's Multiple Stage-plate.-The object of this stage-plate (fig. 19) is to facilitate the exhibition of a series of slides so that they may be observed successively without having to remove and replace each object separately.

The base-plate slides on the stage after the upper stage-plate is taken off, and it holds six slides. Each of these is fixed by two small

screws (passing through the two longitudinal bars) which press the slide against springs attached to the base-plate, there being six springs beneath each bar. The base-plate can be readily pushed in either direction by the hand when it is desired to examine a different object. The mechanical movements of the stage will bring various parts of an object into the field, but it is easy to adjust each slide on the plate in the first instance so that the object shall be central with the optic axis, there being sufficient spare room to move the slide both laterally and vertically.

Stewart's Safety Stage-plate.-This very simple device (fig. 20) was designed by Mr. C. Stewart to provide an economical but

effective arrangement for protecting slides from breakage when being exhibited under high powers to large classes of students.

It consists of a wooden slip the length of an ordinary slide and

rather wider, with a central aperture and two side pieces ( in. high), capped with thin strips of brass projecting at either end of the uprights as shown in the fig. Across the projecting ends two small indiarubber rings are stretched and the slide is passed through these rings and thus suspended. If now the objective is brought down on the slide the latter sinks on the least pressure and ample warning is given to the observer.

Parsons' Current-Slide.—Mr. P. B. Parsons has devised the new form of current-slide shown in figs. 21 (section) and 22 (perspective), which he describes as follows::

"The slide consists of two plates, pierced with central apertures

FIG. 21.

surrounded by tubular projections, and fitting together like a live-box. The top one is raised or lowered by a milled head fixed to the lower one and working in a thread cut on the tube of the upper. Two pins prevent the plates from coming apart or turning on each other.

The top plate has a hole at one end for the water supply and a

FIG. 22.

similar hole on the other for the waste, a piece of movable brass tube fitting into each.

The supply tube has a valve for regulating the quantity of water admitted, and beyond this is an indiarubber pipe connected with the water-vessel. A double-necked bottle is very convenient, so that a fresh supply of any fluid can be introduced without disturbing anything.

The advantages of this arrangement are:

1. The depth of the cell is easily adjusted while on the stage, and the object can be brought within reach of fairly high powers by simply reducing the depth of water to a thin film. When not under examination with such powers the cell can be deepened, giving plenty space with a constant current of fresh water, and yet enabling the observer to keep the object in view with a lower power.

of

2. The diameter of the cell, while large enough for all ordinary