of the Electric Light. Ill 



dark interval may attain a length of 6 centimetres. When the 

 tinfoil or the fingers are caused to glide towards the positive 

 pole, it appears as if the strata in front merge into each othei', 

 whereas they appear to recede from each other if the conductor 

 moves towards the negative pole. 



A very marked effect of conductors on the stratified light is 

 obtained when the fluid of the inductive machine comes into 

 the tube by one of the poles only, the other pole and the other 

 end of the wire being insulated. The luminous strata are then 

 very feeble ; if the tube be encircled by the hand without touch- 

 ing, their diameter diminishes ; they appear contracted towards 

 the axis of the tube, but are more distinct. If the hand be 

 pressed on the tube, or if a piece of tinfoil not insulated be 

 affixed, the light becomes feeble between the conductor and the 

 inactive electrode, but on the side of the active electrode the 

 strata become more brilliant. At the same time, if the active 

 electrode be positive, there appears on this side, at the edge of 

 the tinfoil, a large dark space, as if this edge had become the 

 negative pole. 



The wave of continuous light, obtained by drawing sparks on 

 one end of the tube while the other is in contact with the induced 

 wire, is also influenced by external conductors. The hand which 

 encircles without touching the tube, contracts the wave towards 

 the axis. The contact of the fingers spreads it into a spindle ; 

 and if the pile be not very strong,, the internal light appears to 

 press against the glass in front of the external conductor. In 

 the last case, the tube being simply taken between two opposite 

 fingers, the continuous wave appears to undergo a disruption, 

 and, further, not far from the positive pole, a brilliant layer is 

 seen to be produced. By touching another section with two 

 other fingers, a second rupture is effected, which produces the 

 appearance of a second luminous stratum. Often the stratified 

 wave which occupies that part of the tube near the positive pole, 

 pushes the strata to a junction with those which the influence 

 of the fingers has produced. 



When only one of the poles is active, if the tinfoil which en- 

 velopes part of the tube be touched by the free extremity of the 

 induced wire, the space situate between the tin and the inactive 

 pole becomes much darker, and the other increases in brilliancy ; 

 at the same time there is produced on this part, that is, at the 

 side of the active pole, a system of very complicated stratifica- 

 tions, which may be accounted for by supposing that each time 

 that the haunacr of the induction a])paratus rises, two inverse 

 and successive currents are propagated in the tube. The second 

 of these currents is given by the electricity of the tinfoil, wliich 

 rejoins by the induced wire that of the tube. By raising the 



