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THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



APRIL 1909. 



XLI. The Relighting of the Carbon Arc. By J. A. Pollock, 

 JD.Sc, E. M. Wellisch, M.A., and A. B. B. Ranclaud, 

 B.Sc* 



[Plates IX. & X.] 

 1. Introductory. 



WHEN" the arc between fixed carbons, in a hand-fed 

 lamp, burns itself out, it may be restarted if too 

 great an interval of time is not allowed to elapse, by lessening 

 the distance between the carbon terminals, but without 

 bringing them into contact. Again, if the circuit is broken 

 and reclosed after a short time, the arc may reestablish itself 

 without the carbons being moved. 



In connexion with this latter point, Mr. Upson f has given 

 observations of the maximum times of interruption of the 

 circuit within which the arc will restart, for different arc- 

 lengths and for various previous currents, with carbon- 

 carbon, and with copper-carbon arcs in air, and states that 

 in the circumstances of his experiments copper-carbon arcs 

 in coal-gas and in hvdrogen did not restart. 



The relighting of the arc after a given time of interruption 

 depends, however, not only on the previous current and on 

 the arc-length, but also on the potential-difference established 

 between the electrodes at the moment of reclosing the circuit, 



* Communicated by the Authors : read before the Royal Society of 

 New South Wales. 



T Upson, Phil. Mag. xiv. p. 126 (1907). 



Phil. Mag. S. 6. Vol. 17. No. 100. April 1909. 2 I 



