204 



ANNUAL EEPOKT_ SMITHSONIAN INSTITUTION, 1908. 



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intensity of the current coming over the line, the luminous pencil 

 traverses a part more or less opaque of this " gamut of tints " and 

 the intensity of the light at F consequently varies. According as the 

 reflected ray passes through a dark or clear part of the " gamut " 

 when the style of the transmitter is upon a thin or white portion of 

 the film will the result be a positive or a negative. 



The cylinder, C, of the receiver is inclosed in a dai^v chamber and 

 covered with a sensitive film. A metallic screen, pierced with a hole 

 one-sixth of a millimeter in diameter, is situated at F and limits the 

 extent of the film acted upon by this light. And finally, in order to 



avoid the phenomena of diffraction, 

 a b this pierced, metallic screen touches 



closely the sensitive surface of the 

 film. The reproduced image is formed 

 by the juxtaposition of short lines one- 

 sixth of a millimeter in breadth. 



We would call attention to two 

 special features in the apparatus of 

 Belin. The rheostat, R, is composed 

 of 20 resistances, the values of which 

 are calculated with due allow^ance for 

 the resistance of the line so that a 

 proper variation of the current w^ll be 

 reproduced. These resistances are con- 

 nected to a little commutator com- 

 posed of 20 laminae of silver, sej^arated 

 by leaves of mica. This assembly jdos- 

 sesses a thickness less than St^- milli- 

 meters; ujjon the surface of these 

 laminae works the contact of the lever 

 which is actuated by the relief of the 

 bichromatized gelatin film of the cyl- 

 inder, C. This piece plays an imj)ortant role and is a most delicate 

 part of the apparatus to construct. 



In order to obtain a rapid transmission of the signals it is nec- 

 essary to use a galvanometer, at the same time very sensitive and 

 of a very short j)eriod of oscillation. Belin employed an instru- 

 ment somewhat widely used to-clay in laboratories, the oscillograph 

 of Blondel. This apparatus, represented schematically by figure 7, 

 consists essentially of a flat, extremely fine wire attached between two 

 fixed points, a and 6, and stretched at its lower end by the pulley, ^, 

 which is attached to a spring. The whole of this is placed between 

 the poles PP, in the very intense magnetic field produced by the 

 electro-mamiet EE. Wlien the current mounts in one of the blades 



Fig. 7. — Bloiidel's oscillograph. 



