THE RELIGHTING OF THE CARBON ARC. 215 
THE RELIGHTING OF THE CARBON ARC. 
By J. A. POLLOCK, pD.sc, EH. M. WELLISCH, M.A., and 
A. B. B. RANCLAUD, B. Sc. 
[With Plate XXXVII.] 
[Read before the Royal Society of N. 8S. Wales, September 2, 1908. ] 
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 re- 
establish itself without the carbons béing moved. 
In connection with this latter point, Mr. Upson’ has given 
observations of the maximum times of interruption of the 
circuit within which the are 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 hydrogen did not restart. 
The relighting of the arc after a given time of inter- 
ruption 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, and the object of our experiments 
has been to find the relation between this latter factor and 
the time interval, for carbon-carbon arcs in air at natural 
pressure, under various conditions. 
The maximum time of interruption of the circuit, under 
given conditions, within which the arc will reform on 
* Phil. Mag., xiv, p. 126, 1907. 
