﻿1874.] L. Scliwendlcr— 0;^ tlie General Tlicory of Duplex Telegraphi/ 233 



ADDENDUM. 



niSTOllICAL. 



When reading tills paper before the Asiatic Society on the 4th Fehru- 

 ary 1S74, and, further, when editing the First Part for publication in tho 

 Journal of the Society, I was unacquainted with the fact that a most com- 

 plete history of Duplex Telegraphy had been published by Dr. Karl Eduard 

 Zetzsche* (Leipzig 18G5). According to Professor Zetzsche,t the Bridgo 

 Method of Duplex Telegraphy was already invented in 1863 by Maron, a 

 Prussian Telegraph Inspector ; and Dr. Zetzsche very truly remarks that 

 the Bridge Method would seem to be that least affected by variations in the 

 resistance of the line. To this, from an historical point of view, most valua- 

 ble book, I refer the reader. It is to be hoped that an English translation 

 of it may soon be published. 



year (South- West monsoon) — when necessarily the insulation as well as the inductive 

 capacity of lines are so enormously variable, that about its thorough practicability no 

 doubt can be entertained, and Col. Robinson, Director General of Telegraphs in India, 

 has consequently decided to introduce this duplex method »lso on the other long main 

 lines of India. 



At present the apparatus for the Bombay-Madras line (worked direct 800 miles) ia 

 almost finished, and the apparatus for Calcutta-Rangoon is under manufacture. 



The Calcutta-Bombay main line is worked duplice with Jabalpur only in transla- 

 tion ; distance between Calcutta and Jabalpiu- 8o0 miles : distance between Jabalpm- and 

 Bombay 640 miles. The wii'e is almost thi'oughout No. 5| B. W. G. (diam. = 5| 

 m. m.) 



This experiment, made on such a large scale and under the most unfavorable meteo- 

 rological conditions, has proved most conclusively tho practicability of the double balance 

 method, which certaialy will invariably succeed on any L'^ie where single telegraphy is 

 possible. 



* Die Copiertelegraphen, die Typendrucktelegraphen, und die Doppel Telegraphie, 

 em Beitrag zur Geschichte der electrischen Telegraphie, von Dr. Karl Eduard Zetzsche, 

 Leipzig 1865. 



t Page 125 in the work quoted. 



(To le continued.) 



