144 ANNUAL OF SCIENTIFIC DISCOVERY. 



ure (ov any number of standins: fi2:nre«, — it Ijeing^ one o^reat merit 

 in this plan that a whole group may be introducetl into the land- 

 scape with no more trouble than a single figure), against a black 

 background and upon a black floor, and take the portrait (or the 

 group) on a piece of mica. After fixing and varnishing, apply 

 some thick water color on the back of the mica, behind all the 

 transparent parts of the figure. Outside of the figures all, of 

 course, will be transparent; this is the object of having a black 

 background and black floor. 



'* Now select any view at pleasure. This may be a natural view, 

 or an engraving, or a photographed view on paper (that is, a posi- 

 tive paper print). Prepare one of the pieces of glass as a dry 

 plate. Put it in the dark slide with the mica portrait in front of 

 it, and so expose at the view, engraving, or photograph. Take 

 off the mica, develop the plate, fix and varnish. There will 

 then be obtained a landscape negative with blanks exactly cor- 

 responding to the figures. Then attach firmly to it the mica 

 plate, first, of course, cleaning off the color previously applied on 

 the back of the mica behind the transparent parts of the figures. 

 In attaching the mica, the figures must be m ide exactly to cor- 

 respond with the blanks, and then it is cemented fast. 



'* I think it will be seen at a glance that this method offers some 

 striking advantages over any of the usual plans ; especially in 

 this, that the result is not two negatives to be printed with the 

 utmost care into each other, but a compound negative that any 

 tyro can print as easily as an ordinary one. 



"The atmospheric effects in the print, supposed to be got by 

 faintly and delicately shaded backgrounds, are probably caused 

 by the faint light which comes even from a black background; 

 and, as more of this light is reflected from the upper part of any 

 screen than the lower, this would exactly cause the atmospheric 

 effect spoken of, by throwing a slight haze over the upper part of 

 the picture. At any rate, this effect could be increased as much 

 as might be desired, if found insuflicient. 



" This idea of a double negative, the front piece consisting of a 

 transparent piece of mica carrying the figures, is, I believe, en- 

 tirely new, and, in ingenious hands, might be made to produce a 

 variety of interesting effects, especially in the combinations of ob- 

 jects which cannot, with portrait-lenses, be brought simultaneously 

 into focus, with the advantage, too, of perfect simplicity and ease 

 in the printing." — M. Carey Lea, in the British Journal of Pho- 

 tography. 



ELECTRICITY AND THE SENSTTIYE PHOTOGRAPHIC FILM. 



M. Becquerel finds that chloride and bromide of silver deposited 

 on plates of platinum, when acted upon by light, give rise to a strong 

 current of positive electricity, which is just the reverse of the kind 

 of current which would be afforded by the platinum plate alone 

 under the same circumstances. Now the chloride and bromide 

 of silver are actually decomposed by light, — the former obviously 



