351. My invention is for tracing or sketching for crayon or other portraits. It can be used by any one, and for enlarging any object that can be attached to the top, which is to contain the picture, face down. It can be made for any size, from 8 x 10 to life-size. The tana, the movable front for focussing, clamps for holding the movable top, which is adjusted from inside, and governs the size of the object, and the reflector, to throw strong sunlight on the object, will all be seen in the diagram; also, the table or stand upon which the paper, or material upon which to draw the image as it is reflected down, is placed. This is a very useful instrument for any gallery, as any card can be enlarged to a perfect 8 x 10, or larger, to show the customer how he would appear In a large portrait, which might induce him to have one made. The one I have is intended for a ten-inch head, or from that down to 8 x 10. It is two feet square at the base, four feet high, fifteen inches wide at the centre, with a twelve - inch arm to the reflector. The reflector has three movements, or six, counting the backward movements. The movable box has only two movements, up and down, for governing the size of the reflection. The box is nine inches square, one inside of the other, fastened with a thumb - screw inside of the front curtain. The movable top is raised and lowered from the inside, and fastened by a clamp with a thumbscrew in front. The thumb - screw is ten inches long, to reach clear across the front. ' The strip across the centre, holding the reflector, is eighteen inches long. The box or frame work is covered with soft flannel, and lined with thick yellow paper, so no light gets in save the reflected light It will be observed that the image is very strong, and has the appearance of a finished picture. The rays falling in at the top make it a very pleasant light to work in, just right for comfort, something like twilight. It takes one to trace by measure, as all portraits do on canvas or cardboard, from two to four hours. An artist
352. The popularity which the magic lantern is gaining makes it an advantage to know how to produce transparencies for it, for enlargement upon the screen. True, the best and most interesting subjects come from abroad, but since the modern lecturer scarcely dare appear upon the stage without a lantern to assist him, he must often call upon the local photographer to make special slides for him. The photographer, then, should have a few plain directions how to proceed. If the "wet" process is used, an arrangement similar to that shown in the drawing is employed, two cameras of, say, 8x10 size being placed front to front upon an inclined platform in a room with a southern exposure. The negative is fastened in the upper end, and the holder containing the sensitized plate is placed at the back of the other camera. Careful focussing, clean plates, ripe collodion, exact exposure, and thoughtful development are all needed.
353. The usual size for a lantern slide is 3 1/4x4 1/4 inches. Of course, rarely crayons two heads alike from the same picture, and do his best. I can with this make eight sketches with ten-inch head in less than an hour, and have them alike every time, for I will not change the focus, and pin the paper each time at the same place. Changing the position of the reflector does not change the reflection, as it leaves the picture every tirne alike. This is not usually the case with a solar printer. I am a great friend to the solar camera, but I can, by using a condenser, do the same work by this. - S. L. Platt.
353. A good bromo - iodized collodion tolerably ripe, with a bath in good working condition for negatives, will give good results. We give a full exposure, and develop rapidly with an iron solution containing a large proportion of acetic acid - about fifteen grains of the iron salt and thirty minims of acetic acid to the ounce of water. This gives a transparency in which the deposit is, by transmitted light, of a warm, purple-brown tone. If a blacker tone be required, it is easily obtained by using the gelatino-iron developer, though a black color is not the best. Where a very black tone, both by reflected and transmitted light, is required, toning by means of bichloride of mercury, followed by a dilute solution of ammonia, or of hyposulphite of soda, gives excellent effects. For the magic lantern, transparencies are best toned by a saturated solution of bichloride of mercury, followed by a weak solution of hydrosulphate of ammonia, care being taken to well wet the plate before applying the mercury solution, and wash well between each operation. The color will be determined by the the image should come within this, for a margin must be allowed for a mat. Focus in the centre of the plate, and use the smallest diaphragm. The positives may or may not be toned;if they are, gold may be used, or,better, sulphuret of potassium.After the manipulations are over and the transperancy varnished, a mat and a cover - glass are placed over it, strength of the hydrosulphate of ammonia solution. Experience alone will determine the beat proportion, but about six drops to the ounce of water will be found an average proportion. To teat their suitability for the lantern lay them on white paper; the lights should show only white paper, but the shadows should be perfectly black. The following method of toning transparencies, whether produced on wet collodion or dry plates, gives a rich, warm, brown-black, very nearly resembling the well - known color of the albumen transparencies of Messrs. Ferrier and Soulier. It is necessary to observe that a thin, slightly over-exposed transparency is best suited for the treatment After fixing and washing take a little of the pyrogallic developer, a few drops of the silver solution, and a few drops of glacial acetic acid; pour it on and off the plate until the picture is nearly as vigorous as you require it to be when finished. Wash well, and apply a saturated solution of bichloride of mercury until the image is quite white. Wash again thoroughly. Next take a thirty-grain solution of anmonio - nitrate of silver, and pour it on the plate - it immediately changes to a greenish yellow tint, and gradually darkens; add a drop or two of ammonia, it will hasten the change of color, and very soon the picture will stand out bright and clear, of a brown sepia color. If the transparency be varnished, a fine textureless varnish should be used, and great care used to avoid dust In many cases a greater degree of richness and transparency in the shadows is obtained by varnishing; but where the photograph is perfect, it is better unvarnished, the picture being protected by a thin glass instead. If ground-glass be used at the back, it should be very fine; but the benzole varnish known as "crystal varnish," with two or three grains of white wax to each ounce, forms an excellent substitute for ground-glass, drying semi - opaque with a fine texture. A thin solution of starch applied, but not too hot, also forms an excellent substitute for ground - glass. For the magic lantern, a semi-opaque backing is not, of course, required. - J. Traill Taylor.