46 REPORT — 1869. 



Electricity. 



Descrij)tion of some Lecture- experiments in Electricity *. 

 By Professor G. C. Foster, F.R.S. 



In this communicatiou the author draws attention to the facility with which 

 the transient electric currents accompanying the production and disappearance of 

 electrostatical charge can he detected hy the use of Sir William Thomson's re- 

 flecting galvanometer; and, in illustration, describes the application of this in- 

 strument to the investigation of the action of the electrophorus, and to the comparison 

 of electrostatic capacities and electromotive forces. A description is also given of 

 a simple method of proving the existence of the inverse and direct extra-currents 

 in coiled conductors. 



On the Metallic Deposit obtained from the Induction-discharge in Vacwtm- 

 tuhes. By J. P. Gassiot, V.P.R.S. 



The usual metallic deposit obtained from the discharge of an induction-coil in 

 vacuum-tubes is known to arise from minute particles of the negative electrode, 

 emanating in a lateral direction from the wire ; these are thus deposited on the 

 glass with metallic lustre when examined by reflected light. Such particles are 

 very freely deposited from gold, silver, or platinum electrodes ; less so from iron, 

 copper, and other metals, but not from aluminium, although the latter becomes red- 

 hot and ultimately fuses. 



In one of Geissler's tubes with which I have for some time experimented, I ob- 

 tained, by using my extended series of the voltaic battery, not only a very dense 

 opake deposit on the glass round the negative electrode, but five or six bands of dark 

 deposit along the tube ; in carefully examining their position, I found they exactly 

 coincided with the dark bands between the strite, that they did not increase in 

 density by continuing the discharge like the deposit round the negative, but remained 

 without any further change. 



I have not any record from Geissler as to the nature of the gas with which the 

 tube was originally filled, I therefore requested him to prepare other similar-shaped 

 tubes with the several simple and compound gases he nad previously used, but 

 I have not as yet been able to obtain similar results in any of these vacuums. A 

 short time since, when examining some vacuum-tubes at Messrs. Cetti & Co., my 

 attention was directed to one in which I observed a series of brilliant metallic 

 rings deposited inside the glass; on inquiry Mr. Cetti informed me that the tubes 

 had been originally charged with arseniuretted hydrogen and then exhausted in the 

 usual manner; that almost immediately after he had passed the induction-discharge, 

 the stratifications were much reduced, the beauty, as he described it, of the ex- 

 periment was destroyed, while on the inside of the several lu-anium glass bulbs 

 through which the discharge passed, a thick metallic coating, apparently the metal 

 arsenium, was deposited. 



This result appeared to me to explain that the deposit in Geissler's tube already 

 referred to, did not arise from particles of the negative electrode, but from the gas 

 with which it was originally charged ; and if this is the case, their being deposited 

 exactly in the spaces occupied by the dark portions between the luminous disks 

 may lead to a correct explanation of a phenomenon that has hitherto baffled the in- 

 genuity of the experimentalist. 



On an Electromaynetic Eaperiment. By The Hon. J. W. STRUTif. 



On the Electric Balance. By F. H. Varley. 



* Tliis paper is printed in e.vtensn in the Philosophical Magazine for September 1869, 

 t Vide Philosophic.nl Magazine, tlvily ISC'.). 



