1880.] Dynamo-electric Currents in TelegrapTiy. 171 



main current by A is therefore more advantageous than to produce it 

 by E. Hence I employed A in the final trial. 



The final trial on Sunday 29 th Augikst 1880. — The battery wire, before 

 the trial began, was tested for insulation, and gave an absolute insulation 

 greater than 1 €1 ohm. The main current, as already mentioned, was 

 produced by dynamo-electric machine A ; i. e., from 8'-i)5 to 11'5 hours 

 through the wire coil of resistance r, and from 11-5 to 11 '32 hours 

 through the arc of an electric lamp producing the light J. Tlie light of 

 the lamp was not measured, but may have been equal to about 6,000 

 standard candles.* The first line was connected to the battery Avire at 

 8'4'5 hours ; the last line at 10-53 hours. The whole trial was completed 

 at 11-32 hours. 



The change from r to lamp (J) was made in so short a time that none 

 of the out-stations noticed it. Messages were sent and received in the 

 usual regular style. 



Mr. C. B. P. Grordon, the Superintendent of the Bengal Division, 

 attended at the Signal Office. 



At the beginning of the experiments, the resistances in circuit were 

 measured. 



Internal resistance of dynamo-electric ) „ . , i ^ fcj 



, . , ' ^ w = 0-652 internal ^ 



macliine A J i ira 



Wire coil 



Leading wire to tangent ) 



r = 1-517 "I |- 1^ 



j jf _ o-0''6 J ■'■^^'^ external 



galvanometer i ^ J J 



o 



After the experiments were over, these resistances were not measured 

 again ; however, on account of the very considerable heating by the strong 

 main current, they must, we know, all have increased considerably. 



When r closed the poles of the dynamo-electric machine (8-45 to 

 11-5 hours) the mean speed of the engine was eO^^ revolutions per 



minute ; — !— ' = — ; while the mean deflection of the main-current was 

 min. 5G' 



r.^ro 40-251 

 87-87GS ; = ——J. 



mm. da 0^ 



When the lamp was in circuit (from 11-5 to 11-32 hours), the mean 



max. 61 



speed of the engine was again 60^^ ; — r— ^ = — : while the mean deflec- 

 ^ . mm. 59 



max. 46^ 



tion of the main-current was 44^''', = -— r . 



min. 421 



In the following table all the results are given : — 



• When measured under 45° with the horizon. 



