1880.] 



Dynnmo-electric Currents in Telegraphy. 



160 



i. w. g.j and thence to the Calcutta Telegraph Office it is American com- 

 pound wire of the same resistance as iron wii'e of Xo. 27 i. w. g. 



At the Calcutta Telegraph Office, the hatferi/ ivire* could at a moment's 

 notice be connected with the key of each instrument, after throwing off the 

 copper of the signalling battery in ordinary use. The telegraph lines 

 terminating at the Calcutta Office were therefore all connected parallel to 

 the battery wu'e, as is indicated in the foregoing diagram. 



In order to enable me to directly compare the signalling current sent 

 into the lines by batteries and by a dynamo-electric machine, each line 

 is as tested for sent current at Calcutta, and for received current at the 

 out- station. 



Freliminary trial on 2Sf7i August 18S0. — The line used for tapping 

 the signalling current was Xo. 5, Calcutta to Allahabad, 577 miles in length, 

 worked direct and having a real conduction resistance of about 3075 ohms, 

 (taken from the August 1880 tests). The resistance of the relay at 

 Allahabad equals 492 ohms. 



\st Experiment. — This consisted in taking the sent ciirrent at Cal- 

 cutta and the received current at Allaliahadj as produced by a battery of 

 60 minotti-cells connected up in series. This is the usual signalling bat- 

 tery during the monsoon. 



'ind Experiment. — The main current in this experiment was produced 

 by dynamo-electric machine Af through the resistance r. The resistance 

 in circuit was not measured, but may be taken to be as follows : — 



m = 0-652 \ internal. 



Leading wire to tangent galv. I — 0'026 / J external 



r = 1-517 ohms at 85° F. 



\ 7 = lo4>n 



Total, 2-195 ohms. 



The main current gave a mean deflection of 37-9' 



max. _ 39 

 min. — 36^ ' 

 max. 62 



mean speed of engine 60-3 revolutions per minute : — : — = . The 



^ ° ^ ' mm. 58-5 



variation of the current corresponds with the variation of the speed. 



Srd Experiment. — The main current in this experiment was produced 



by dynamo-electric machine E. j through the resistance r. This experi- 



* The Telegraph liae conveying the current produced by the dynamo-electric 

 machine to the Telegraph 0£B.ce may he called most appropriately the battery wire. 



t This is a Siemens' dynamo-electric machine called medium size (see my precis 

 of report on the electric light experiments in London). 



i This is a Siemens' medium machine altered according to my specification 

 (See precis of report on the electiic light experiments in London) . 



