the Spectra of Argon 81 



condenser and a variable induction were then placed in the 

 primary circuit. By varying the amount of the capacity 

 together with the self-induction in the primary system, the 

 discharge in the secondary, when examined by a revolving 

 mirror, was seen to consist of both red and blue discharges. 

 The red glow was evidently caused by a unidirectional dis- 

 charge, and the blue by an oscillatory discharge. The 

 unidirectional discharge was due to the failure of the breaks 

 to charge the condenser of the primary, or to increased resist- 

 ance in the tube. When, however, the condenser was charged 

 it immediately discharged in an oscillatory manner ; and the 

 secondary coil responded by resonance. The rarified argon 

 thus shows in an interesting manner what is the function of 

 the condenser in the primary of an induction-coil. It serves 

 to send oscillatory discharges through the primary circuit; 

 and the greatest effect is obtained in the secondary circuit 

 when it is in resonance, or in tune so to speak, with the 

 primary. 



The presence of a condenser was necessary to form the 

 blue glow in Kayser's work, only when the resistance of his 

 tube and the self-induction of his coil together were enough 

 to damp the discharge of the small capacity of the coil. He 

 could have obtained the pure red in any case by interposing, 

 as we have done, a resistance or self-induction between the 

 condenser and the tube, although our other resource for 

 obtaining the red glow in any tube from the continuous dis- 

 charge of a constant battery was apparently not open to him. 

 By taking out all resistance except the spectrum-tube, and 

 sending an exceedingly strong current through the tube for 

 very brief intervals of time, we have been able to cause the 

 blue glow ; but it seems probable that under these conditions 

 the capacity of the battery itself engenders oscillations which 

 are no longer damped by interposed resistance. Whether 

 the blue glow with its accompanying change of spectrum is 

 due merely to the great quantity of electricity discharged in 

 a very short space of time, or to some property intrinsic in 

 the to-and-fro motion of the oscillatory discharge, is a question 

 which we hope soon to answer. The red glow, if caused by 

 oscillations at all, must be caused by oscillations within the 

 Geissler tube itself*; for all outside oscillations are cut off by 

 the large resistance between the battery and the tube. 



The effect of the oscillatory discharge in producing the blue 

 spectrum of argon can also be shown by the use of an elec- 

 trical machine. If the terminals of the tube containino- argon 



* Ann. der Phys. und Chem. 1893, vol. xlviii. p. 549. Ebert and E, 

 Wiedemann. 



