Wireless Transmission of Photographs / Second Edition, Revised and Enlarged 1919

by Marcus J. Martin

J, screen; L, Nernst lamp; G, shutter; B, condensing lens; B₁, focussing lens.

When, however, signals are sent out from the transmitting apparatus, the magnified current from the relay U energises the coil of the special telephone S, attracting the diaphragm F, and consequently giving movement to the pivoted rod R. As by means of the optical arrangements a

magnified movement as well as a magnified image of G is thrown upon the screen J, the shadow of G will, when the telephone S is actuated, cover the hole in the screen, and prevent any light from reaching the film on V, until current from the relay U ceases to flow. Therefore, when the stylus of the transmitter traces over a conducting strip on the metal print, no light reaches the film on V, but when tracing over an insulating strip the shadow of G on the screen J rises, and the light from L reaches the film. By this means a positive picture is received, which is a great advantage where the photographs are required for reproduction. Atmospherics would be represented by irregular transparent marks on the film after development, and these can be easily eradicated by retouching.

The drum of the machine moves laterally ¹/₇₅th of an inch per revolution, and the hole in the screen is ¹/₉₀th of an inch in diameter. As the screen J is not in direct contact with the film, the slight diffusion of the light that takes place will produce

a mark of about the right thickness. With a movement of the diaphragm of only ¹/₄₀₀₀₀th of an inch, the actual movement of G will be ¹/₄₀₀₀th of an inch. If the optical arrangements have a magnifying power of 100, then the movement of the shadow upon the screen will be ¹/₄₀th of an inch, which will be ample to cover the aperture.

The aluminium rod R, minus the counter-weight, can be made to weigh not more than 12 grains. It is necessary to enclose the optical parts in a light tight box, indicated by the dotted lines in Fig. 43, in order to prevent any extraneous light from reaching the film.

The Contact Breaker.—The contact breaker (L, Fig. 35), as will be seen from Fig. 44, consists of an electro-magnet N, the windings of which are connected with the battery B and the polarised relay K. The armature which is supported by the spring G carries a contact arm A, which in its normal position makes permanent contact with the contact screw T, and completes the circuit between the relay K and the telephone relay U (Fig. 35). As soon as the transmitter sends out the first signal, the magnified current from the telephone relay actuates the relay K, which in turn completes the circuit of the contact breaker. Directly the armature M has been attracted, the contact with T is broken, and A makes fresh contact with the screw H, by means of the spring Z

fastened to the underside of A. The armature, once it has been attracted, is held in permanent contact with H by the catch S, independent of the magnets N. As soon as contact is made with H, the clutch (F, Fig. 35) circuit is completed, and the circuit of the relay K is broken. When the circuit of the clutch F is broken by means of the circuit breaker C on the machine (Fig. 36), the stop S is pulled back by hand, allowing the contact arm A to rise, and again make fresh contact with the contact screw T.