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Page:Popular Science Monthly Volume 44.djvu/59

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51
ELECTRICITY AT THE WORLD'S FAIR.

excess of letter carriage, it can apply only in cases in which important interests are involved and dispatch is of moment. Such instances are, however, growing increasingly frequent in the modern business world, so that the telautograph, if it prove as successful in actual commercial work as it has in experimental tests, will not lack for a large and profitable field.

The attempts to realize facsimile transmission go back almost to the beginning of telegraphy. As early as 1846 Alexander Bain attempted such reproduction by means of trailing contacts passing over the face of metallic letters at the transmitting end of the circuit, and like contacts sweeping over a chemically prepared paper at the receiving end. When the contacts were on the faces of the letters a current was sent to line; and these current impulses, decomposing the chemical preparation of the receiving paper, made brown or blue marks, according to the nature of the chemical solution, which reproduced in broken outline the original letters. This method of operation was ten years later much improved by Caselli, who transcribed the message or sketch to be sent on a metallic-faced paper, and caused a stylus actuated by a pendulum to traverse in succession all parts of the design. A similar stylus reproduced the drawing or writing on chemically prepared paper at the receiving end. Many attempts have been made by subsequent inventors to adapt this method of transmission to commercial work, but without success. All systems of this kind, it will be observed, depend upon the establishment of exact synchronism between the transmitting and receiving instruments, and this is a condition very difficult to realize in practice. Moreover, the message must first be written either in a special ink or on a special paper, and afterward transmitted, which renders the process slow and necessitates expert knowledge to operate it.

The telautographic method proceeds upon entirely different lines. In this the movement of the transmitting pencil in the hand of the operator causes electrical impulses to be sent over the line, which impulses, through the medium of appropriate mechanism, act upon the receiving pen and cause it to duplicate the movement of the sending one. The possibility of doing this depends upon the geometric principle that the movement of a point in describing a plane curve, no matter how intricate, may be resolved into two rectilinear movements at right angles to each other. In order, therefore, to have the pen at the receiving end of the line follow all the motions of the transmitting one, it is only necessary to resolve the movement of this latter into its right line components and reproduce them at the further end. A point situated at the focus of these lines of movement will then describe the exact motions of the original one. Simple as this