of Electric Light. 273 



that with one giving 5' sparks, the latter are filled with light. 

 Mr. Gassiot found the same eiFect from increasing the number 

 of battery cells ; and I believe that his gigantic American machine 

 scarcely shows any stratification. 



But even were it universally true that a spark of sufficient 

 length interposed in the circuit prevents the appearance of 

 strata, still Mr. Grove's theory of their origin would remain 

 subject to weighty objections. We have no experimental evi- 

 dence that the cuiTent which he supposes to succeed the extra 

 current in the primary coil, exists with any sensible energy; 

 and, granting its existence, it is not easy to see how it can pro- 

 duce the eflFects assigned to it ; for, apparently, it must be sub- 

 sequent to the discharge of the secondary coil, and therefore 

 cannot modify that in any way. A. synchronous one, we know 

 from experiment, only weakens the force of another that is op- 

 posite; and in the static discharge, where there is the very 

 system which he requires, a discharge followed at a very small 

 interval by a weaker opposite one, there is certainly no special 

 power of developing strata. 



A different view of their origin, and one which seems nearer 

 the truth, is given in the Number of ' Cosmos ' for the 4th of 

 last month, by M. Morren of Marseilles. He thinks they are 

 caused by periodical variations of intensity in the current, due to 

 the resistance which it meets in traversing an imperfect con- 

 ductor, and that these cause lateral discharges of the conducting 

 material ; he therefore compares them with the wings that pro- 

 ject from the stains made by exploding fine wires over paper by 

 an electric battery. The notice is so brief, that I supposed he 

 meant to represent these explosion-pictures as " autographies 

 des stratifications de lalumiereelectrique;" but the meaning of 

 this phrase is made clear by another notice in the same journal 

 (Feb. 18) from M. Seguin, who also seems to have obtained the 

 same result. An induction spark sent along glass dusted with 

 fine charcoal, leaves a track whose markings he considers iden- 

 tical with the strata. Undoubtedly these variations of intensity 

 do exist : they are shown by the fracture of a wire into minute 

 pieces when the discharge is not quite sufficient to fuse it, and 

 still more plainly by sending the static discharge of a powerful 

 induction machine through a fine steel wire some feet long. 

 In air of ordinary density, and still more in rarefied air, the wire 

 is luminous ; but at every inch or two it throws out a circle of 

 brushes. In the exploded wire, or the air over the glass, the 

 same thing happens ; but the brushes carry with them most of 

 the metallic vapour or the charcoal dust, leaving a deficiency of 

 them at the intermediate points. On repeating M. Seguin's 

 experiment, I obtained the appearances which he describes: 



