NATURAL PHILOSOPHY. 165 



toward completion ; all that remains to be done, is to transfer it on the 

 lithographic stone. For this purpose the stone should be finely pol- 

 ished with wafer and pumice stone ; then the waxed silk covered with 

 a few sheets of unsized paper, is pressed down tightly with a screw, 

 but not too much. For greater success, the stone is warmed, and the 

 whole left in the press for several hours, to give the lithographic ink 

 time to react upon the stone. It is evident, wherever the photogenic 

 coating covers the silk the lithographic ink cannot act upon the stone, 

 and besides, its dryness will prevent it from sticking, so that when the 

 silk is taken off, the stone will be clean wherever it touched. There 

 remains nothing else to be done but to submit the stone to a slight 

 acidulation with a large quantity of gum arabic. Actually, the result 

 of taking the copy will be quite different from what it would be with 

 the plate engraved by means of acids. Every portion of silver uncov- 

 ered, and represented on the waxed silk by a continued coating of 

 lithographic ink, will produce on the stone an oleaginous place of the 

 same extent, which will give the shading. It is for the purpose of not 

 erring in the other extreme, that the waxed silk should be covered 

 with an infinitely fine coating of lithographic ink, to prevent its 

 destruction, which might blur the lights and shades. 



FIXATION OF COLORED PHOTOGRAPHS. 



M. NIEPCE DE SAINT VICTOR laid before the Paris Academy of 

 Sciences, at the sitting of the 8th of November, daguerreotypes upon 

 which he had succeeded in fixing, in a manner more or less perma- 

 nent, colors by the camera obscura. ]\I. Xiepce states, that the pro- 

 duction of all the colors is practicable, and he is actively engaged in 

 endeavoring to arrive at a convenient method of preparing the plates. 

 " I have begun," he says, " by reproducing in the dark chamber 

 colored engravings, then artificial and natural flowers, and lastly dead 

 nature a doll, dressed in stuffs of different colors, and always with 

 gold and silver lace. I have obtained all the colors ; and, what is still 

 more extraordinary and more curious is, that the gold and the silver 

 are depicted with their metallic lustre, and that rock-crystal, alabaster, 

 and porcelain, are represented with the lustre which is natural to 

 them. In producing the images of precious stones and of glass we 

 observe a curious peculiarity. We have placed before the lens a deep 

 green, which has given a yellow image instead of a green one ; whilst 

 a clear green glass placed by the side of the other is perfectly repro- 

 duced in color." The greatest difficulty is that of obtaining many 

 colors at a time; it is, however, possible, and M. Niepce has frequently 

 obtained this result. He has observed, that bright colors are produced 

 much more vividly and much quicker than dark colors : that is to 

 say, that the nearer the colors approach to white the more easily are 

 they produced, and the more closely they approach to black the 

 greater is the difficulty of reproducing them. Of all others, the most 

 difficult to be obtained is the deep green of leaves ; the light green 

 leaves are, however, reproduced very easily. After sundry other 



