384 SUMMARY OF CURRENT RESEARCHES RELATING TO 



is facilitated by a counterpoise. After lowering the lamp lens Kj should 

 be thrown out of action, and the lamp placed at such a distance from 

 lens K, that the pencil of rays emerging from the latter, after reflection 

 at the inclined mirror placed below the stage, may entirely fill the lens 

 let into the stage. The reversing mirror G sends the light through 

 objective Q, whereby an image is formed on the screen. 



Lettner, G. — Skioptikon Einftihrung in die projektionskunst. 



Leipzig (1907) 105 pp. (22 figs.). 



(4) Photomicrography. 



Reversible Photographic Proofs ; Integral Photographs.* — Under 

 the above titles G. Lippmann discusses the principles which must 

 underlie the production on a single film of such an effect as would be 

 equivalent to the actual view obtained of a landscape by an observer 

 through a window, the film yielding the same varieties of effect as would 

 be afforded by slight changes of position on the part of the observer. 

 The author thinks that the practical difficulties to be overcome may not 

 prove to be insurmountable. It is necessary to imagine a film as ordi- 

 narily used, formed of a transparent pellicule of celluloid or of collodion, 



Fig. 110. 



treated on one of its faces with an emulsion sensitive to light. Before 

 spreading the emulsion on the pellicule, suppose that the latter has 

 been pressed while hot in a kind of goffering machine, in such a 

 manner as to produce on each of its faces a large number of small 

 excrescences in the shape of spherical segments. Each of the excrescences 

 with which the anterior face (this face will remain bare of emulsion) is 

 intended to act as a convergent lens. Each of the excrescences of the 

 posterior face is covered with a sensitive emulsion, and is intended to 

 receive the image formed by one of the anterior lenses. Fig. 110 shows 

 an enlarged section of a film thus constituted. In order that each image 

 may be in focus, corresponding segments must have the same centre of 

 curvature, and the ratio of a front ray to a back ray must be n — 1, where 

 n is the index of refraction of the celluloid for rays photographically 

 the most active. The system formed by any one whatever of the small 

 front lenses, and by the portion of sensitive layer corresponding to it, 

 forms a small camera like an eye, the lens being the cornea and the 

 sensitive layer the retina. There is no crystalline, and none is required, 

 for, in virtue of its small diameter, the tiny camera can remain sensibly in 

 focus on every object, however slight its distance. If the term " cellule " 

 be applied to each such elementary camera, it follows that the complete 

 pellicule is a tissue of these cellules juxtaposed. If each cellule be a, 



* Comptes Rendus, cxlvi. (1908) pp. 446-51 (2 figs.). 



