ELECTRICITY AT THE WORLD'S FAIR. 51 



excess of letter carriage, it can apply only in cases in wliich im- 

 portant interests are involved and dispatch is of moment. Sucli 

 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 pass- 

 ing 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 im- 

 pulses, 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 origi- 

 nal 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 transmis- 

 sion 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 instru- 

 ments, 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 ren- 

 ders the process slow and necessitates expert knowledge to oper- 

 ate 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 



