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682 THE PHOTOGRAPHIC NEWS. [October 26 figure by arranging a properly-shaped pattern over said head in correct relation to the same, and then exposing that portion of the print on which the new groundwork is to be formed to the action of light, substantially as set forth. 3. That method of forming groundwork for new figures or dresses, or for darkening the latter, which consists in placing a transparent plate over a photographic print, laying a cut-out or pattern in proper position over said print on said plate, then securing said pattern in place by a second transparent plate, and finally exposing said print with its superposed plates and pattern to the action of light, substantially as described. 4. That method of rendering a photograph of a light or rough dress dark or smooth in appearance, which consists in covering a photographic print with a pattern, which is cut away so as to expose only such dress, and then subjecting the exposed picture of the dress to the action of light to darken or smooth the same, substantially as set forth. 5. A cut-out or pattern for forming groundwork for new figures in photographic prints, such pattern having a cut-away portion conforming exactly in shape to the outline of the pro posed new figure, substantially as described. 286,447. Benjamin W. Kilburn, Littleton, N. H., assignor to the Scovill Manufacturing Company, Waterbury, Conn., “ Photographic camera.”—Filed March 30,1883. (No model). Claim.—1. In an apparatus for taking instantaneous photo graphs, the combination of a photographic camera and a support therefor having the form of a gun, and provided with a shoulder- piece, the camera being mounted on the support in such a posi tion that a photographic plate placed in it will be approximately at right angles to the length of the support, substantially as specified. 2. In an apparatus for taking instantaneous photographs, the combination of a photographic camera and a support therefor having the form of a gun, the camera being so arranged upon the support that a photographic plate placed in it will be approxi mately at right angles to the length of the support, and being detachably connected with the support, so that it can be removed and used on a different support, substantially as specified. 3. In an apparatus for taking instantaneous photographs, the combination of a photographic camera and a support therefor having the form of a gun, the camera being mounted above the support in such position that a photographic plate placed in it will be approximately at right angles to the length of the support, and the camera being elevated sufficiently to leave between it and the support an unobstructed passage, affording provision for sighting along the barrel-like portion of the support, substanti ally as specified. 4. In an apparatus for taking instantaneous photographs, the combination, with a photographic camera provided with a fly- shutter, of a support having the form of a gun, on which the camera is mounted in such a position that a photographic plate placed in it will be approximately at right angles to the length of the support, the said support being provided with a shoulder- piece, and means connected to the shutter and extending along the support nearly to the shoulder-piece, so that they may be actuated to effect the release of the shutter, substantially as specified. Specification Published during the Week. 1095. J. W. Tattersall, “Apparatus forwashing photographs.” The object of this invention is to wash photographs on paper and glass more expeditiously and more effectually than hitherto. I accomplish my object in the following manner : I construct a casing of zinc, tin, wood, or other suitable material for a small business, and for large businesses—I fit up a room. Into the ease or room as the business requires, I so arrange piping con nected with the town’s main or other water supply, with jets, so constructed as to break up the water issuing from such jets into fine spray ; this spray is brought into either direct or indirect contact with the photographs, which in one case I place upon trays above the outlet for overflow, and in the other somewhat below, such overflow. I know of no mode of washing by any apparatus which will accomplish the effectual washing in less than four hours; by my improved apparatus I can effectually wash photographs in less than thirty minutes.—Provisional protection oiilp. — • LESSONS IN OPTICS FOK PHOTOGRAPHERS. BY CAPTAIN W. DE W. ABNEY, R.E., F.H.S. Aplanatic lenses and flatness of field.—This gives a flat ness of field, which is secured by the use of a diaphragm placed at a proper distance from a lens. W e have brought this example forward, since we have found that the common idea of an aplanatic lens is that of a lens which gives a flatness of field. An aplanatic lens is one in which spherical aberration is corrected for rays parallel to the axis; that is, a lens with which the whole aperture of the lens can be used for bringing a distant point lying on or near its axis to a sharp focus. It is formed by the com bination of two or more lenses, the simplest form being a combination of a convex with a concave. In treating of spherical aberration, we stated that the rays refracted from the margin of a lens meet on the axes closer to the lens than those coming from the central portion, and we took an example of a convergent lens. If, however, a con cave lens be used, the rays from the margins of the lens cut the axis of the lens closer to the lens than do the central rays. Suppose we combine a concave lens and a convex lens together, we may still have a convergent lens, but one in which the central rays and the rays from the margins may meet at the same point on the axis, and therefore have the same focus. This can be effected by properly adjusting the curves of each lens. A lens so corrected is an aplanatic lens. We shall see in another lesson that there is another aberration besides spherical (viz., chromatic) which has to be corrected. It sometimes happens that in correcting one aberration, the other is over- or under-corrected. If the negative (i.e., concave) lens makes the marginal rays of the combination cut the axis further from the lens than where the central rays cut, it is over-corrected, and the lens is said to have negative spherical aberration. If tbe marginal rays cut the axis closer to the lens than the central rays, it is corrected too little, and is said to have positive spherical aberration. A lens can be tested by using diaphragms such as given in figs. 23 and 24, Lesson IV. The effect of the thickness of lens on its focal length.—We have hitherto treated a simple lens as if it had no thick ness, that is, as if it were a plate made up of very minute concentric rings each having a section of a minute prism. Practically (and unfortunately, too, for some things), a lens has a sensible thickness which one cannot afford to neglect. Photographic single lenses are, however, as a general rule, thin, and a rule-of-thumb correction can be made for the thickness which gives tolerably correct results, viz-, to • Continued from page 619.