PHOTOTELEGRAPHY AEMAGNAT. 



203 



THE TELESTEREOGRAPH OF BELIN. 



The system of Belin is far simpler and requires, besides photog- 

 raphy, only purely mechanical devices, such that in the trials, al- 

 though they were only local and with no attempts at synchronism, it 

 was possible for him to furnish more practical results than those 

 obtained by Korn, despite the ingenuity and the much-praised devices 

 of the latter. 



As we have just said, Belin did not wish to complicate his experi- 

 ments with the problems of synchronism, knowing that there now 

 exist many tried means of solving that part of the problem, and he 

 contented himself with coupling mechanically the transmitter and 

 the receiver side by side. 



The picture to be transmitted is reproduced upon a bichromate 

 gelatin film. Rej)roductions of this kind are known to be much 

 thicker where the light has acted the most intensely, and consequently 

 a photograph on such a bichromate gelatin film has a variable relief. 

 This property has, 

 indeed, been made 

 use of in some of 

 the processes of 

 photo-engraving. 



The bichroma- 

 tized-gelatin film 

 is rolled at G (fig. 

 6) upon a cylin- 

 der, C, which has a double movement of rotation and translation as 

 in the preceding apparatus. A lever, jointed at its upper part, carries 

 a style analogous to those used with phonographs, and resting firmly 

 upon the film, follows all the reliefs of the latter. These displace- 

 ments of the style are magnified eight times by a lever near its lower 

 extremity ; the end of this lever forms a minute contact which moves 

 over the bars of a rheostat, R. The circuit incloses a battery, the 

 rheostat, R, the line and the receiving apparatus. According to the 

 value of the relief at the point touched by the style, the resistance 

 taken from the rheostat is more or less great, and so the intensity of 

 the current in the line varies. At the receiving station the apparatus 

 consists of a galvanometer, O, whose mirror receives light from a 

 lamp. The pencil of rays reflected from the galvanometer falls upon 

 a lens so placed that the light which traverses it is always brought 

 to a focus at the point, F, upon the photographic film, A. Before 

 the lens there is placed a screen, T, composed of twenty strips of 

 increasing capacity, called by Belin a " gamut of tints." According 

 to the deflection of the galvanometers, that is to say, according to the 



Fig. 6. — Bella's apparatus. 



