which, after careful filtration, is poured over a well cleaned and dusted glass plate. After draining a little by standing on blotting paper, dry over a spirit lamp, and place, while still warm, under a negative in the printing frame—one minute in the sun, 10 to 20 minutes in the shade, is about the necessary exposure. As previously mentioned, the shorter the exposure, the denser will be the resulting negative, a result at variance to any other photographic printing operation. To develop the picture the glass plate is placed, coated side upwards, upon a sheet of clean white paper, then, with a soft camel-hair brush, dust over the picture some very finely-ground Siberian graphite, working the same backwards and forwards over the plate until the necessary strength is attained. If the picture should develop too quickly, and take the colour all over, the cause is under exposure; should the powder adhere unevenly, or the picture present a smudgy appearance, the coating must have absorbed too much moisture, and must be again warmed before further development. This precaution is particularly necessary during the winter months. If a prolonged development be necessary, and after continuous dusting a picture lacking in contrast be the result, it is occasioned by over exposure. On completion of the development the picture should be finally and carefully dusted with a soft brush to remove the superfluous powder, coated with a thin plain collodion, and placed in water, which should be frequently changed, until it fails to show any trace of yellowness. The plate should be afterwards retouched and varnished. =Negative Films= have now been before the public some time, and have been considerably used as reversed negatives by printing with the back of the film in contact with the plate. The four principal varieties are, in the order of their introduction—1st, Eastman’s; 2nd, Froedman’s; 3rd, Pumphrey’s.