156 THE ELECTRIC TELEGRAPH. 



brium, previously established by the equating battery, is 

 destroyed ; and the relay of A will give a signal corresponding 

 to the length of time which B keeps down his key. During 

 also the whole time that A keeps down his key, the relay of 

 B will be affected, whether the key at station B be pressed 

 down or not, because, as we have seen, the effect of his own 

 current on his relay is neutralised by his equating battery. 

 If, therefore, both stations work their apparatus at the same 

 instant, signals will be given properly by the respective 

 relays. 



There is only one position in which a perfect reception of 

 the signals transmitted from one station is not attained by 

 the other. It is when, during the manipulation at either of 

 the stations, the lever of the key is removed from the back 

 contacts, c c', until it touches the front contacts, a a, or vice 

 versa. In these cases the line circuit is interrupted for 

 an instant at b, and the signal which should be given by the 

 relay of the same station is disturbed. 



This is, however, a small evil compared to the great diffi- 

 culty in retaining the compensation of the line and equating 

 batteries for any length of time. The plan adopted by 

 Gintl, of using a thicker and shorter coil on his relay for the 

 equating circuit, occasioned the equating battery to expend 

 itself quicker than the line battery, which encounters con- 

 siderably more resistance ; and this continued diminution of 

 the intensity of the compensating current, whilst the line 

 battery kept nearly constant, caused a corresponding effect 

 on the home relay, which gave the operator often some of 

 his own signals back again, if he does not continually see 

 to the strength of the currents. 



93. This system was first used on the line from Prague to 

 Vienna, but difficulties soon induced Gintl to forego the 

 attempt to work Morse instruments by this method, and to 

 adopt instead a chemical telegraph, by which he obtained 

 much better results.* 



The plan of this modification is shown in Fig. 86, in 

 which' a b is the line wire from one station to the other, con- 

 * " Dub's Auwendung, &c.," p. 461. 



