1880.] 



Dynmno-eJeetrie Currents in Telegrapfiij . 



173 



After the dynamo-current was stopped at 11'32 hours, and the bat- 

 teries had been connected up again, the sent currents at Calcutta and 

 the received currents at outstations were again ascertained Hence columns 

 5 and G contaiir 3 readings of sent and received currents for each line ; 

 first, with battery, secondly, with the dynamo-electric machine, and, thirdly, 

 ■with the battery again. All the readings of the currents tapped from the 

 main current of the dynamo-electric machine were taken between 8'45 

 and 10'53 hours, when the iron wire coil of resistance r was connected to 

 the poles of the dynamo-electric machine. From 11'5 to 11'32 hours, 

 when the lamp was substituted for r, no current readings at Calcutta and 

 the outstations were taken. 



The main current of the dynamo-electric machine, when r was in 

 circuit, was 36,801 m, o ; when the lamp was in circuit, 45,706 m. o.* 

 From this it does not follow, however, that the tapped currents in the 

 second case were larger than in the first, because it would also depend on 

 the resistance offered by the arc, which is not known. The resistance of 

 the arc, as more current was produced with the same speed of the dynamo- 

 electric machine, must naturally have been smaller than r =■ 1-517 b. a. u. 

 (iron wire coil), especially as there is an e. ni. f. in the arc opposite 

 to the e. m. f. of the dynamo-electric machine. 



To produce 36,801 milli-oersteds through an external resistance of 

 about 1'543 b. a. u., a total energy is consumed by the dynamo-electric 

 machine of about 27,000 Q ergs per second (representing about 3 h. p. 

 per second). 



Conclusions. — These experiments shew that it is perfectly possible 

 and practicable to tap from the main current produced by a dynamo-elec- 

 tric machine all the signalling currents required at the Calcutta Telegraph 

 Office. These currents were for the 11 lines connected up = 129'1 m. o, 

 if all keys were simultaneously and permanently sending. This represents 

 only 0'35 of the main current (36,801 m. o) with r in circuit, and 

 •28 °/o of the main current (45,706 m. 6) with lamp in circuit. Further 

 it will be clear that such a small variation of the main-current could not 

 influence the regularity of any work done by that main-current. 



Further, it will be seen that in all the exj^eriments the sent currents 

 tapped from the main current of the dynamo-electric machine were 

 considerably larger than when produced by the large batteries at present 

 in use. Experiments IX and X only form an exception. However, 

 1 think these exceptions are in both cases due to errors of observation, be- 

 cause the battery readings in Experiment IX do not all agree. The 

 dynamo-current readings in No. X must be wrong, because in No. XI, 

 for a total circuit resistance of 7759 units, the sent current is 13 38 m. o, 

 • Calcutta by the formula : e = 47330 to (m. 0"J. 



