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SCIOPTICON MANUAL. 65 ty, and as free as possible from all defects. As the magic lantern slide is generally 3J x 3J, it is not desir- able to employ a very large negative. 6£ x 8£ will answer the purpose better tban a larger size. But neg- atives upon smaller glass will be found to give even finer results. On the other hand, it is very bad policy to attempt to enlarge a positive to double or treble the size of the original negative. The negative should not be smaller than the positive. The Lens. —Any good portrait combination, of six to eight inches focus, quarter-inch stop, will work to ad- vantage. Lenses of very short focus and very small opening, are not recommended. The Development —Should be conducted with great care and judgment, as it is the most important part of the whole process. Rather underexpose and underde- velop, and as soon as the detail is visible, flood the plate with water, and check further action. Avoid an excess of light during development, and dread the appearance of the slightest fogging as the worst enemy to be en- countered. Fixing Solution. — Cyanide of potassium, after which wash well in running water. Toning. — It is frequently of benefit to the positive that it should be toned, and at the same time slightly strength- ened, to give contrast to the picture when projected upon the screen by a powerful light. Many chemical solutions may be used to accomplish this purpose. A weak solu- tion of gold gives good results; also, a dilute solution of bichloride of palladium can be recommended. In either case the solution is flowed over the plate, after fixing. The positive is then dried and varnished. The Finished Picture —Should be free from the slight- est appearance of fog; the high-lights, the sky in land-