36 THE SCIENTIFIC PAPERS OF 



telegraphic communication between the tender and tug employed 

 in laying the last Mediterranean cables. 



My summary of telegraphic novelties would not be complete 

 without a notice of a method of sending messages simultaneously 

 in both directions through one and the same line wire, the joint 

 invention of the Hanoverian telegraph engineer Frischen and my 

 brother. It consists in splitting the current of the battery into 

 two equal parts, of which the one proceeds through the line 

 and the other through an adjustable resistance coil by a short 

 circuit to the earth. Both currents pass in opposite directions 

 round the relay magnet of the communicating station, and 

 neutralise each other in effect, but the portion of current pass- 

 ing along the line wire, produces an effect upon the relay at the 

 receiving station, and vice, versa, but if both stations include their 

 batteries at the same time, the current of the line wire will be 

 doubled, and in exercising a preponderating effect upon both 

 relay magnets, will cause both to attract their respective arma- 

 tures, and establish the printing circuits. By this means, the 

 transmitting power of a single line wire is doubled. This system 

 works satisfactorily between Amsterdam and Rotterdam, and some 

 other places where there is not much interference by intermediate 

 service ; but it is, I consider, as yet too refined for general appli- 

 cation. The same objection applies to a system of accelerating 

 the speed of transmission of messages by preparing strips of 

 perforated paper which, in passing between a metallic roller and 

 contact finger, break and restore the metallic current with un- 

 limited rapidity, a system first introduced by Bain years ago. 

 These plans will probably be of great practical utility eventually, 

 when the use of the electric telegraph is more extended. 



In conclusion, I have to thank the meeting for their patience 

 in listening to this paper, which far exceeds the limits I had 

 assigned to it. I have to express my special thanks to Professor 

 Wheatstone, Mr. Latimer Clark, Dr. Green, Mr. Edward Bright, 

 and Messrs. Newall & Co., for their liberal aid in furnishing me 

 with models to illustrate the subject. 



I wish to draw particular attention to the key and relay 

 arrangements of Mr. C. Varley, used upon the Dutch cable, 

 and the acoustic telegraph, worked by secondary circuit, used 

 by the British Magnetic Telegraph Company, which lack of 



