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XLVI. On the New Electromotive Force in the Voltaic Arc. 

 By E. Edltjnd*. 



WHEN a luminous arc is formed between two charcoal 

 points by means of a powerful voltaic battery, and the 

 circuit is broken in any place on one side of the arc so that the 

 current ceases, and if the circuit be completed after a brief in- 

 terval, the luminous arc is not extinguished, though the current 

 was interrupted for a short time. The time during which the 

 current may be thus interrupted without extinguishing the arc 

 depends upon the intensity of the current. With a strong cur- 

 rent the time may be longer; with a weak one the time must be 

 reduced if the arc is to continue. If the same experiment be 

 made with a luminous arc between silver instead of carbon poles, 

 the light is extinguished at the moment of interruption, and 

 does not spontaneously reappear when the circuit has again been 

 restored. This deportment of the light between carbon poles 

 doubtless indicates that the conduction in the arc lasts a short 

 time after the cessation of the current, by which it is possible 

 that the current, when the break on the side of the luminous arc 

 has been restored, can reproduce the arc. If the conduction 

 had been quite destroyed during the short break, the incipient 

 current would not be able to traverse the path between the car- 

 bon poles and renew the light. But the conduction in the lu- 

 minous arc is principally produced by detached particles which 

 are carried by the current from one pole to the other. It must 

 hence be assumed that in the first moment after the break in the 

 conduction the particles of carbon are being continually detached 

 and carried from one pole to the other. 



In a previous investigation I have proved that the mechanical 

 work which the current consumes in order to disintegrate the 

 poles gives rise to an electromotive force which sends a current 

 in the opposite direction to the principal current f. If, now, this 

 disintegration lasts for a short time after the cessation of the 

 principal current, it may be possible to separate the current 

 resulting from this electromotive force from the principal one, 

 and measure it free from all action of the latter. With this 

 design I have made the following experiments in common with 

 Dr. Lemstrom, of Helsingfors. 



2. To break the circuit on the side of the arc, a commutator 



* Translated from a separate copy communicated by the Author, having 

 been read before the Royal Academy of Sciences at Stockholm, January 

 1868. 



t Phil. Mag. S. 4. vol. xxxv. p. 103. 



