376 EXPERIMENTAL INVESTIGATIONS. 



to refer to his memoirs ;* I have done so since making the 

 experiments given in this Postscript, and find that with regard 

 to the rings so formed by electrolysis he suggests interference 

 as a possible explanation. 



The dark space in the discharge to which Faraday has 

 called attention may possibly be connected with these pheno- 

 mena. I have observed that in a well-exhausted receiver, 

 containing a small piece of phosphorus, the discharge is 

 throughout its course striated by transverse non-luminous 

 bands, presenting a very beautiful effect, and a yellow deposit, 

 which, as far as I have yet examined it, seems to be allotropic 

 phosphorus, is deposited on the plate of the air-pump and on 

 the neighbouring substances ; to show this effect well the 

 needle should be positive and the plate negative, and the 

 distance between them about an inch. 



I could dilate much farther on these experiments, but have 

 already trespassed perhaps too far for a postscript. Variations 

 in the form of the terminals, in the nature of the gas, vapour, 

 or gaseous mixture, in the density of the gas, in the intensity 

 and quantity of the discharge, in the nature of the plate, &c., 

 will occur to those who may feel inclined to pursue these ex- 

 periments, and, if I am not over-sanguine, promise results of 

 much interest. 



ADDITIONAL NOTE ON THE DARK DISCHARGE. 

 Phil. Mag., Dec. 1852. 



I find the transverse dark bands can be produced in other 

 gases when very much attenuated, probably in all ; and I 

 rather think the reason why they are more easily seen in the 

 phosphorus vapour is, that all the oxygen having been 

 consumed, a better vacuum is formed. 



In addition to these bands, and under circumstances where 

 they are barely visible, there is always seen a well-defined dark 

 space intervening between the glow surrounding the negative, 

 and the stream of light proceeding from the positive terminal ; 

 it appears independently of the length of the discharge, though 



* Ann, de Ch. d de Phys., vol. xxxiv. 



