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January 9, 1885.J THE PHOTOGRAPHIC NEWS. 23 found one plate broken. Next took a group. Arranged the people very nicely, &c., but forgot to pull slide out of holder. Next took two couples, and left holders on my table. On coming up after lunch, found that some inquisitive person had opened one of the slides and let in the light. I then went down to develop. The image seemed to come out very fairly ; then put negative in hypo bath, and it gradually grew darker from the edge, until only a slight shadow remained in centre, which would not come out. According to instruction, I then washed thoroughly, rubbing gently with my fingers. Door, panels, &e., were distinctly visible before, but when I’d washed thoroughly, never a sign of a picture was there at all. Cleaner piece of glass was never put into a gentleman’s spectacles. The second one showed no sign of a picture, but remained a melancholy black from the beginning. I was determined not to be beaten, so took two more of the doctor, and have brought out some sort of a picture, but don’t think they're right—they look too filmy to be correct. I tried to take a print from one, but the glass must have been damp, the paper stuck to it, I could get no impression. September 30th.—This morning I tried again, and a picture appeared on the blue paper ; but the moment I put it in water, the blue immediately left the paper, and it shortly appeared as white as the opposite side. 11 A.M.—Have just tried a second blue print. Before washing, the picture was a fair one, but, like the last, the paper became entirely clean when washed in the basin. 5 P.M.—The same thing had happened again. This time I thought possibly the print should be washed in the dark room ; but the photo., which appeared a very fair one, was entirely washed off. I then tried with the other paper. Some of it had evidently seen the light. I had to mix two baths for it, and produced fairly satisfactory results. I can’t for the life of me think what is up with that blue paper. I’ve followed instructions, I think. October 1st.—There’s something the matter with the blue paper or the manipulation, I feel confident. I’ve tried it again, and the colouring leaves it directly it touches the water, coming off in a yellow sediment. This shuts me up until further instructions are received. October 5th.—Developed two more negatives yesterday, and tried several experiments with the blue paper this morning. Among other things, I scraped one of the negatives considerably in one corner, and then tried to print on blue paper, leaving in a good sun for about an hour. The result was the same as in previous cases, viz., the whole sheet washed as white as your shirt-front, except the scratched portion, where the paper became a deep blue. This confirms my supposition that the negatives are not right; there’s too much of that thick glutinous stuff on them. THE MICROSCOPE FOR CLASS-ROOM DEMONSTRA TION. BY W, 0. THOMPSON, M.D. Tub following adaptation of the use of the microscope as a sort of magic-lantern for class demonstration has been found so ex tremely useful, cheap, and practical, that it is illustrated here. A large common kerosene “ duplex ” lamp is the illuminator. Superfluous light is cut off by a piece of six-inch stove-pipe, which fits over the lamp-chimney, and rests upon a horizontal collar C, of stove-pipe metal. The collar prevents the pipe from shutting down too far upon the lamp, which would cause the kerosene to become dangerously hot. The lamp is filled at F with a curved glass funnel; and the two flat wicks, an inch and a-half broad, are turned by their separate keys outside of the pipe. The pipe has two elbows, which conduct heat and smoke away, and completely cut off the light from the top of the flame. These elbows may be rotated into any convenient position. Opposite the lamp-chimney a third short elbow, F, is inserted, closed by a movable cap. Through this elbow the chimney can be removed, the wicks trimmed, and a concave glass or tin re flector, M, four inches and a-half in diameter, may be placed behind the flame. The flat of the wicks should be parallel to this mirror. Opposite the mirror, and directly in front of the flame, a plano-convex lens, A, two inches in diameter, is inserted in a hole in a pipe. The light reflected from the mirror, N, passes through this lens, and falls upon the reflector of the microscope, whence it is made to illuminate the object upon the glass tlid e in the ordinary way. The object is magnified by a one-fifth inch or one-half inch objective; the eye-piece of the microscope is removed; and the image is projected upon a ground-glass screen, G, a foot and a-half square, which is placed from one to four feet in front of the microscope. The screen is supported by a perpendicular iron rod and cork-lined clamp, such as is in use in every chemical laboratory, to hold glass retorts, tubes, &c. The iron rod rests upon the floor, occupies very little space, and can be moved to any convenient focussing distance. A similar stand supports the horizonal elbow of the stove-pipe. The tube of the microscope should be blackened inside as in micro-photography. The microscope is handled in every way as usual in respect to stage movement, fine adjustment, &c. The great difficulty with the apparatus consists in trying to prevent the reflection of superfluous light. To obviate this, a pasteboard box, B, six by six by eight inches, is readily cut to fit closely over the plano-convex lens, and the back of the micro scope stage, thus enclosing the microscope reflector, and allowing it room to be focussed properly when the lid of the box is re moved. It is also advisable to fit a sheet of pasteboard, F, tightly over the microscope tube at right angles to it, in order to cut off the rays which escape around the object illuminated, pass along the axis of vision outside of the tube, and tend to blur the image on the screen. B, outline of paper box to enclose mirror ; C, collar to support stove pipe ; E, elbow through which chimney may be removed; E, funnel for filling lamp; G, ground-glass screen; M, reflector inside of stove-pipe (posterior surface); P, paste-board screen ; X, hole in stove-pipe where lens is inserted. Dr. J. West Roosevelt (to whom the larger part of the inge nuity of this apparatus is due) and the writer have for some time made constant use of it for instructing students. Physiological, histological, pathological, and botanical specimens may be clearly shown. A number of students can look on at once. The slides are rapidly changed, and students and instructor may always be sure that they are discussing the same particular cell; which, unfortunately, is not the case when a beginner in the use of the microscope looks through the instrument alone. The apparatus may readily be constructed by any one for about five dollars ; it is easily portable, and always ready for use many darkened room. It is possible to throw the light from the lens X directly upon the object without the intervention of the microscope reflector, but the reflector facilitates focussing. Objectives of wide aperture are preferable. With some lenses, the use of the eye-piece adds distinctness, but in most cases it cuts out too much light. An Abbe illuminator may be inserted. The image on the screen G is seen most distinctly upon the farther side; and some objects become clearer if the screen be moistened with water, or covered with a thin coat of transparent varnish laid over the ground sur face. The image may also be received upon white glazed paper, but this is less clear. For demonstration on a larger scale, an oxy-hydrogen light can of course be used, or some form of electric light. The arc-light is not sufficiently steady, and the incandescent light requires a great deal of storage-room for batteries. The light above de scribed shines with thirty-six candle power, is clear and steady, and serves every ordinary purpose ; the circulation in the frog’s foot, varieties of epithelium, injected lung tissue, tubercle, plant cells, &c., may all be clearly shown. The colours of stained or injected specimens come out distinctly. The principle of this apparatus is by no means new; but its application is made so easily within the reach of any one who owns a microscope, that it is especially recommended to instructors in schools and colleges.—Science.
