THE 



AMERICAN JOURNALOFSCIENCE 



[FOURTH SERIES.] 



Art. XI. — On the Electric Arc between Metallic Electrodes /* 

 by W. G. Cady and G. W. Vinal. 



Second Paper. — Theory and Production of Oscillations betioeen 



Arc and Glow. 



§ 1. In the first paperf it was shown that in the electric arc at 

 small currents, under certain conditions, the current instead of 

 remaining constant is subject to pronounced and rapid changes. 

 These results proved that Lecher's conclusions regarding the 

 continuity of the electric arc can no longer be accepted without 

 modification. 



The method described in the first paper for testing the con- 

 tinuity of the arc discharge consisted essentially in the use of 

 a bolometer connected in parallel with a self -inductance in the 

 arc circuit. It was found that when the bolometer circuit, 

 consisting of a Wheatstone bridge with a fine Wollaston wire 

 of 10 ohms resistance as one arm, was entirely disconnected 

 from the arc circuit, the galvanometer of the bridge some- 

 times showed a deflection. As this occurred even when the 

 two circuits were a meter apart, it was evident that oscillations 

 of considerable frequency and intensity must be taking place 

 in the arc. 



The study of these- oscillations forms the subject matter of 

 the second and third papers. It will be dealt with under the 

 following heads : 



* This investigation was carried on with the aid of a grant from the 

 Elizabeth Thompson Science Fund. 



f W. G. Cady and H. D. Arnold, this Journal, clxxiv, p. 383, 1907. Some 

 months after the appearance of our first paper, Buisson and Fabry (C. R., 

 cxlviii, p. 1143, 1908) also announced their discovery of the first and 

 second stages in the iron arc. 



Am. Jour. Sci.— Fourth Series, Vol. XXVIII, No. 164.— August, 1909. 



7 



