On the Stratifications of the Electric Light. 109 



first, the ball to be steady and the electric current to pass. Now 

 push the ball forward — there is rupture of contact and a spark 

 behind the new point of contact ; a nipple suddenly emerges from 

 the metal at the point where the spark occurs and pushes the 

 ball forward. It is doubtless to this incessant rupture of con- 

 tact that the crackling noticed by Mr. Gore is due. Mr. Gore 

 confines his attention to electric conduction ; but bad conductors 

 of electricity are also bad conductors of heat — at least among 

 the metals. That a bad conductor of heat produces a better 

 effect than a good one, is a perfect illustration of the justice of 

 Faraday's remark regarding the influence of bad conduction in 

 the experiment of Trevelyan, namely, that it confines the heat to 

 the neighbourhood of the surface, and therefore increases that 

 local expansion which keeps up the motion. — J. T. 



A 



XV. Note on the Stratifications of the Electric Light. 

 By Messrs. Quet and Seguin*. 



S the cause of the luminous stratifications obtained with 

 RuhmkorfF's induction apparatus is not yet known, it is 

 perhaps not useless to endeavour to reproduce the ph?enomena 

 from other sources of electricity, and to modify them by means of 

 external agents. Messrs. Grove and Pliicker have already tried 

 the action of the magnet on the stratified light. 



Stratifications obtained with the Electric Condenser. 



If a Leyden jar be discharged through a cylindrical Geissler's 

 tube, a wave of light is obtained which is usually dazzling, and 

 in which stratifications are not observed. After the first dis- 

 charge, it is easy to obtain two or three others, each of which 

 gives a wave of stratified light throughout the length of the 

 tube : the same phrenomenou is obtained at the first discharge 

 if the jar be feebly charged. 



The luminous stratifications may be produced by converting 

 the Geissler's tube into a condenser by means of a covering of 

 tinfoil. The tube is charged like a Leyden jar, by ])assing the 

 electricity of an ordinary plate machine, either into the very rare- 

 fied gas which it contains, or on to the armature of tin, the second 

 conductor of the tube being placed in communication with the 

 eartli. The discharge of this apparatus produces in the tube a 

 wave of stratified light ; and strata are seen cither on the covering 

 of tinfoil, or on the part of the tube left exposed between tlic 

 envelope and the electrode which is discharged on it. After the 

 first, four or five other feebler discharges may be produced, all 



* Translated by Dr. E.Atkinson, from the Comptes Rendus, December 13, 

 1858. 



