348 Mr. J. Trowbridge on the Oscillations of 



one half. This reduction was due not to the increased self- 

 induction but to the increased resistance ; for the introduction 

 of a water-resistance of some megohms diminished in a similar 

 manner the distance between the stratifications. In short, I 

 could not discover any connexion between the law t = 2ir y'LCI 

 and the phenomenon of stratification. 



I have said that we can pass by insensible gradations from 

 the condition of the brush-discharge to that of the disruptive 

 discharge. By intercalating a non-inductive water-resistance 

 and a vacuum-tube between the terminals of a suitable trans- 

 former, we can exactly imitate the phenomena observed when 

 the vacuum-tube is held in one hand while the other hand 

 grasps one terminal of the transformer. In this case the 

 water-resistance takes the place of the resistance of the air of 

 the room. The intensity of the discharge being thus much 

 diminished, one can readily study various manifestations of 

 stratification which may, perhaps, be termed transitory strati- 

 fications in distinction to the stationary wave-like forms 

 observed in narrow tubes. The transitory stratifications can 

 be produced at will by touching suitable points of a vacuum- 

 tube with the finger or by connecting such points with the 

 ground. Such stratifications are stationary as long as the 

 ground connexion is maintained, and are independent of the 

 rate of the alternating machine which excites the transformer. 

 It is evident that the condenser action of the vacuum-tube 

 plays an important part in this phenomenon. In observing 

 the striae and columnar form of the waving of the light 

 excited in this manner in vessels or tubes filled with rarefied 

 gases, one is led to believe that the stratified form of the 

 Aurora Borealis is produced in a similar manner. Fig. 3 

 (PL III.) is a form of the Aurora noticed by me ; and let us 

 suppose that a discharge of electricity takes place in rarefied 

 air between A and B, and that C is a region of cloud or 

 moisture. C can be regarded as the finger or earth-conductor 

 which is applied to the tube of rarefied air, and which serves 

 to throw the discharge into transitory stratifications and to 

 give the waving form of the Northern Lights. 



The pulsation, therefore, of the Aurora is in no way, I 

 believe, connected with any phenomenon of the oscillatory 

 discharge ; yet certain writers have intimated that the glow- 

 ing of vacuum-tubes which are connected with only one 

 terminal of a transformer and the light of the Aurora are due 

 to millions of electrical oscillations per second. Now it is 

 impossible to study the question of the rate of oscillation of 

 the brush-discharge by means of Feddersens method, for 

 the light of the discharge is not sufficient to produce a 





