Popular science monthly . Fig. 13. The lightshield which is sol-dered to the upright of the film orplate from which the print is to be frame is then held at a distance ofabout 6 ft. from a 25-watt tungstenlamp, and the latter turned on for twoseconds. This exposure is correct forthe average negative and is cited merely. Scnsivs muit^not touch ^R^

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Keywords: ., bookcentury1800, bookdecade1870, booksubjectscience, bookyear1872