488 Mr. Warren De La Rue [Jan. 21, 



instead of 200,000, the strata are reduced in number and turn pink. 

 The plienoraenon, except as regards colour, is shown in the plate 

 (Fig. 6), copied from a photograph obtained in three seconds. 



Tube 130, a hydrogen vacuum 0*8 millimetre, with 2400 cells 

 and an interposed resistance of 60,000 ohms. A series of tongue- 

 shaped strata are produced, which cross each other like the com- 

 ponents of the letter X and remain perfectly steady. The phenomenon 

 is precisely like that shown by another tube, the photograi:)h of which 

 you saw projected on the screen. Tube 130 is represented in the 

 plate (Fig. 6) ; it is copied from a photograph obtained in two and 

 a half seconds. 



Tube 333 is a hydrogen vacuum, pressure 0*8 millimetre, with 

 3G00 cells and an interposed resistance of 1,500,000 ohms. There 

 are produced a series of double tongue-shaped strata, united at their 

 narrowest parts. This phenomenon is represented in Fig. 5 in the 

 plate, which is copied from a photograph obtained in three seconds. 



Before showing the next tube, I will exhibit one (No. 51) with a 

 carbonic acid vacuum, in which the negative terminal consists of 

 a wire nineteen inches long formed into a helix, the positive 

 Fig. 25. being a ring. On passing the current from a battery of 

 1200 cells through the tube, first interposing a resistance 

 of 500,000 ohms, about two inches only of the negative is 

 illuminated ; on gradually, however, removing the resist- 

 ance, more and more of the spiral negative glows until at 

 last the whole of it is brilliantly illuminated. It will be 

 seen by this that the negative discharge requires a greater 

 outlet than the positive. 



I will now exhibit a tube (No. 163), Fig. 25, consisting 

 of two branches united at the top and bottom. In each of 

 these is a series of funnels, the broad end of which fills the 

 branch ; in one branch the mouths of the funnels are placed 

 in a contrary direction to that in the other. On connecting 

 the terminals with the battery of 3600 cells, the current is 

 free to pass either in both branches, or through one or the 

 other, but it invariably passes down that branch in which 

 the wide mouth of the funnel is towards the negative. It 

 traverses alternately the right or left hand branch, according 

 as I make the top or bottom terminal negative ; thus again 

 exemplifying the necessity for a greater space for the nega- 

 tive discharge to pass than is required for the positive. 

 The phenomenon is shown in Figs. 11 and 12 in the plate. 



The photographs from which the figures in the plate are 

 copied were taken in my laboratory, by Mr. H. Reynolds, 

 on dry plates. 



Very frequently, w^hen the exhaust is very great, the 

 discharge becomes most sensitive to the approach of the finger or 

 any conductor in connection with the earth, or charged by a sepa- 

 rate source of electricity ; the same thing occurs if the current is 



