My favourite instrument is shown at Fig. 3. Here the focussing of the lens is effected by rack and pinion work, by means of the screws on each side the upright pillar. The lens is shown fitted in the collar which carries it. The stage is of glass—roughly, 2½ in. long by 2 in. wide, and the arm at the top of the pillar can be moved from side to side, so as to bring a fairly large object within range. The metal framework of the stage is furnished with nickelled clips (not shown), which serve to hold an excavated slip. The arm-rests are detachable, and the uprights are hinged for convenience of packing. The instrument (with the exception of these rests) packs into a neat, strong mahogany box, 7½ in. in length, and about 5 in. in height and width. With two powers—1 in. and ½ in. are very serviceable ones—the cost is 38s.
Fig. 3.—Leitz’s Dissecting Microscope.
It is to be wished that the maker would devise some plan by which the admirable lenses sold with this instrument could be utilized for the pocket. Mr. C. Curties, of Baker & Co., High Holborn, has kindly done something in the matter, and has made for me a metal holder. I have found this convenient, but should be glad to see something further done in the same direction, so that instrument, lenses, and holder could be sold for £2. This ought to be within the range of practical optics. The spring collar advocated by my friend Mr. Wright seems better, and would certainly be cheaper. The lenses would only need to be dropped in. To use my pocket holder one must unscrew the metal collar from the lenses before screwing them into the metal plates which carry them (Fig. 4). It is, however, something to have made a beginning: it is a step in the right direction.
Fig. 4.—Two Leitz Lenses in holder (open).
Fig. 5.—Two Leitz Lenses in holder (closed).
A serviceable dissecting microscope—not a toy, but an instrument with which real work may be done—can be made at a cost of a few shillings. Such a one has been made for me by a friend with a positive genius for such work. The body is fashioned out of a parcel-post box 7 in. long, 3½ in. in height, and the same in width. From the centre of the sliding top a piece is cut away, leaving ledges to take a 3 in. by 1 in. excavated slip for small dissections, or a mounted slide of a large object, such as a whole insect, for examination. A further portion is cut away on each side to take a small dissecting dish (Fig. 6). To admit the light, a hole is cut in the side of the box; and the mirror consists of a piece of silvered glass which was bought of a hawker in the street. This is placed in the box opposite the square hole, and sloped at an angle of 45°. The aid of a skilled mechanic was sought for a small rod carrying a thread, which works in a piece of brass bent at a right angle. This piece of brass is screwed on the box, just above the aperture by which light is admitted, and carries a pocket magnifier, similar to that shown at Fig. 1.
