PHOTOTELEGEAPHY- — ARMAGNAT. 



205 



and descends in the other, one of the blades tends to displace itself 

 perpendicularly to the plane of the figure forward, and the other 

 backward; this causes a rotation of its mirror and it is this latter 

 movement which is used for sending the reflected beam of light 

 upon the suitable part of the " gamut of tints." In order to have a 

 more exact idea of the dimensions of this galvanometer, let us sup- 

 pose that the poles of the electro-magnet PP, are separated by about 

 1 or 2 millimeters, that the wire is a ribbon of bronze about 0.02 

 to 0.03 millimeter in thickness and 0.10 to 0.20 millimeter breadth 

 and finally that the space between the blades is of the order of 0.1 of 

 a millimeter. Such an instrument would have a period of oscilla- 

 tion of about two or three ten-thousandths of a second. 



As has already been said, Belin has never made any but local 

 trials, the line being looped upon the apparatus. Experiments have 

 been made with a 

 line from Paris, 

 through Lyons, 

 Tulle, Bordeaux, 

 Angouleme, and 

 back to Paris, a 

 distance of about 

 1,717 kilometers. 

 With these con- 

 ditions and a 

 spacing of about 

 one- sixth of a 

 millimeter be- 

 tween the traces 



he could reproduce a photograph 13 by 18 centimeters in twenty-two 

 minutes, which, supposing the figure to be composed of points one- 

 sixth of a millimeter on a side, would correspond to G43 signals per 

 second. Belin tried also the transmission of a landscape, which to our 

 knowledge Korn never did ; but it seems that he tried to get a trans- 

 mitted picture in too bold relief and that the spacing of one-sixth 

 of a millimeter is too small, especially if the result is to be used for 

 impressions by the photogravure process. By spacing the traces a 

 little farther apart and augmenting the speed of rotation it would 

 seem possible to obtain beautiful results and a greater velocity of 

 transmission. 



APPARATUS OF BERJONNEAU. 



Berjonneau used as a transmitter a stereotype plate hatched simi- 

 lar to those used in similigravures. This is rolled upon the cylinder 

 D (fig. 8) ; all the points of its surface pass under the point of its 



Fig. 8 — Berjonneau's apparatus. 



