lS2 



NATURE 



{Dec. 28, 1876 



and so placing the indicator between these as to cause 

 them to neutralise each other's effect upon it. 



The credit of reviving the lagging interest in duplex 

 telegraphy appears to be due to Mr. Joseph Barker 

 Stearns, of the Western Union Telegraph Company, 

 United States, who, in 1868, experimented on the New 

 York to Boston line, and subsequently achieved con- 

 siderable practical success on the overland lines of the 

 company with which he was connected. In 1872 Stearns 

 came to England and patented his system, which prac- 

 tically embraced the differential and Wheatstone baJance 



methods, as described, with the addition of a novel sending 

 key and a condenser attached to the rheostat or artificial 

 line. 



With the differential method his arrangement is as 

 shown in Fig. 4, where K is the new sending key, and C 

 is the condenser. The advantage of Stearns's key is 

 that the manipulating lever, a (which is permanently con- 

 nected to the battery b), makes contact with the lever b 

 (which is permanently connected to the receiving instru- 

 ment), before b is disconnected from the earth wire "w, 

 so that, in sending, the line may always be "to earth," 



either through the battery B, or the earth wire w. Thus 

 the evils of both Gintl's and Frischen-Siemens's methods 

 are obviated, inasmuch as the line circuit is not only 

 never interrupted, but the resistance of the earth connec- 

 tion may be kept the same by keeping w equal to the 

 resistance of the battery. In order to prevent the wasting 

 of the battery while it is short-circuited for a moment 

 through the key, the resistance, w', may be added to the 

 battery resistance, and w then made equal to both. 



The condenser was applied, as in the experiments made 

 under Newall's patent, to correct the effects of the static 

 induction of the line upon the instrument. Condensers 

 or accumulators had been in common telegraphic use 

 for producing induction since Bagg's patent in 1858 and 



R I 



Fig. 2. 



Varley's in i860, and it is obvious that the sudden induc- 

 tive charge and discharge of the line could be counter- 

 feited by attaching a condenser or other inductive 

 apparatus to the artificial line. This inductive effect is 

 in general only sensible on land-lines upwards of 300 

 miles long. The induction between the wire and earth is 

 then sufficient to maintain a sensible static chai-ge on the 

 wire, independently of the signalling currents, so that on 

 working the sending key, and thus charging the line, the 

 sudden static charge is for a moment added to the sig- 

 nalling current or dynamic charge : and, on the other hand, 

 when the key is made to earth the line, this static charge 



Fig. I. 



flows back again out of the line to earth. Thus two 

 sudden jerks or " kicks," as they are called, are produced 

 on the electric balance, and false signals are thereby 

 made. When, however, a condenser or other inductive 

 apparatus is added to the artificial line, so as to give it 

 induction, too, the charge and discharge " kicks " of the 

 artificial line may be made to counterbalance those of the 

 actual line. In short, it is clear that if the electrical 

 properties of the artificial and of the actual line in induc- 

 tion, resistance, and insulation are approximately equal, 

 a duplex balance can be effected between them. 



Stearns's key and earth connections were subsequently 



to IJarlh 



Pre. 3. 



NaesJ 



in the same year (1872) re-invented by Herr J. F. 

 of Rotterdam. 



In 1873 Mr, George Kift Winter, Telegraph Engineer of^ 

 the Madras Railway of Arconum, British India, patented 

 in England a method of duplex ^by opposed batteries, a 

 principle which it appears had been previously applied 

 by Mr. Moses G. Farmer, of New York, in 1858. Winter's 

 method consisted in keeping the batteries" at both ends 

 of the line continually applied to it, so that their like 

 poles opposed each other and a standing balance was 

 maintained on the receiving instrument at either station, 



