The Electrical Transmission or Pictures

Abstract

THE art of the transmission of a picture or drawing by electrical means from a given place, so that it can be reproduced in another, may, speaking generally, be said to date from the perfection of Bain's early chemical telegraph about 1842. In its original form Bain's apparatus was devised for purely telegraphic purposes for the reproduction of the given message at the distant station: with this in view, the message was set up in metal type at the transmitting station, and was connected up with a battery, a number of metallic contact brushes, and a series of line wires between the two stations, so that by moving the brushes across the metallic letters a series of electrical impulses was sent out along the various wires, depending upon the form and arrangement of the letters. At the receiving station a similar series of metallic brushes was passed over the surface of a paper strip, soaked in a solution of potassium iodide in starch, with the result that whenever a brush at the transmitter rested upon a metallic part of a letter a current flowed through the corresponding line and through the wet paper strip at the receiver, decomposing the KI solution and giving a blue stain through the reaction of the free iodine with the starch. The resultant marks therefore corresponded with the form of the letters arranged at the transmitting station.