the frame is the brass pan E. Near the centre of this pan is a well, 1 inch in diameter and 2 inches deep. At one side of the well is a clamp, 4, which by the screw 1 is pressed tightly against the specimen to be cut. Over this pan is the iron tripod T T (see Fig. 2), beneath which is suspended a brass plate A by means of the bolts 8 and 9.

This plate is made to incline more or less towards the glass plate C, and is fastened firmly in position by the set screws 11 and 12. By these any desired inclination can be given to the cutting blade, which is clamped to the under surface of the plate A. He commonly used a wide Le Coulter razor blade for cutting. The legs of the tripod have ivory pins driven firmly into holes drilled deep in their ends; these

pins project one-fourth of an inch, and their points, 3, 4, 5, rest on the glass plates C and D. From the sides of two of the legs ivory pins project in the same way, and their points, 1 and 2, rest against the glass B. The opposite sides of the well are grooved on their outer surfaces, and in these grooves rest brass guide-pieces, which are firmly bolted to the frame X X, and connected with these guidepieces is a screw, the point of which presses against the lower part

of the bottom of the well. The threads of this screw are forty-eight to the inch, and the circumference of its head is divided into fifty equal parts.

Fig. 2 represents the tripod seen from below, showing the ivory points 1, 2, 3, 4, 5, the brass plate A, and the blade K fastened by the clamps m and n.

Fig. 3 shows the shape of the heads of the bolts 8 and 9, Fig. 1, and the manner in which they are let into the plate A.

Fig. 4 represents a section through the pan, showing the arrangement of the well W, clamp L, and screw for raising the pan. H is a rubber tube, leading from the bottom of the well, for drawing off the alcohol in the pan after using the instrument.

FIG. 5.

Fig. 5 represents the frame X X seen from below, showing the pan, well W, screw F, rubber tube H, and brass guide-pieces, and the manner in which they are attached to the frame.

The ivory points being well oiled, fill the pan with alcohol, so as to cover the top of the specimen O; place the tripod over the pan, and as far to the left as possible; turn up the screw F until the top of the object to be cut reaches the blade; push the tripod forward from left to right, and the blade will shave the top of the preparation; draw the tripod from the glass B for half an inch, or raise the leg of the tripod resting on D half an inch; it can then be pushed to the end of the glass plates from which it started without the knife touching at any point. Now let the tripod approach the glass B until the points 1 and 2 touch the glass; turn the screw F so as to elevate the pan more or less, according to the desired thickness of the section; again repeat the moving of the tripod as already described, and a section is obtained of uniform thickness and any desired thinness the blade is capable of cutting. With a well hardened specimen and a very thin, sharp blade, sections three-fourths of an inch wide, 1 inch long, and 1-2400th part of an inch thick can readily be made. Very delicate objects need to be imbedded in wax or paraffin; ordinary ones are held by the clamp L without any such preparation.

The whole instrument weighs about 16 lbs., and costs about twenty-five dollars, not including the blades. The cost of four or five blades is not far from five dollars, or one dollar each.

Electrical Mounting Table.-Mr. F. M. Rogers, of Moorgate Station Buildings, E.C., communicates the following:-Microscopists who mount their own objects must have felt the want of a mounting table that would automatically run at any desired rate of speed, while allowing the mounter free use of both his hands. The instrument represented in the woodcuts, which has been devised by him, supplies these requirements, the motive power being electricity, derived preferably from a small and very inexpensive bichromate battery.

Upon joining up the two connecting wires from the battery to the terminals marked A, Figs. 6 and 7, a current flows through the insulated wire A2 surrounding the bar of soft iron B, which is pivoted to the spindle D, and carries the table E. The bar is thus rendered powerfully magnetic, and instantly turns towards the top of the nearest inclined armature, of which there are six, C2 (Fig. 8), cast

in the case C. By means of a circular contact-breaker F, Fig. 7, fixed to the spindle D, but insulated from it, the current is only allowed to excite the magnet when its poles are at the foot of any of

the inclined armatures; as it turns towards the top, or point nearest its poles, the current ceases, and with it any retarding action upon the magnet. Acquired momentum carries it to the foot of the next

FIG. 8.

C

incline, and the process is repeated, a steady rotary motion resulting, which can be regulated by exposing more or less of the zinc in the battery to chemical action.

English Microscope for Students of Mineralogy and Petrology. -Mr. Frank Rutley describes a new Microscope, specially suited for mineralogical and petrological research, constructed for him by Mr. T. W. Watson, of Pall Mall.

An examination of one of the Microscopes devised by Professor Rosenbusch and manufactured by Fuess, of Berlin, showed that, although that instrument possessed many features of great merit, it

also had certain defects which could be best overcome by adopting and modifying a good English model.

The great defects in most of the Microscopes built on the continental patterns consist in their fixed vertical position, the smallness of their stages, and, very commonly, in the absence of any means of coarse adjustment, except by a sliding movement of the body or tube, which, if working stiffly, is very inconvenient, while, if sliding easily, it is apt to be shifted by a very slight touch.

The instrument now manufactured by Mr. Watson is in most respects quite equal in performance to Rosenbusch's, so far as the mechanical appliances and adjustments are concerned, and is, in point of convenience, decidedly superior to the latter instrument.

The general form of the instrument is sufficiently shown in the accompanying woodcut. In the stand first made the milled head of