314 Royal Institution. 



To make evident to the audience the relation of the electrical dis- 

 charge to combustion and the fact that the terminals were themselves 

 affected, the voltaic arc was taken, first between silver and then be- 

 tween iron terminals : in the first case a brilliant green-coloured 

 flame was produced ; and in the second a reddish scintillation or spur 

 fire effect, just as in the ordinary combustion of the metals. 



So with the discharge of Franklinic electricity between the same 

 two metals, a strip of silvered leather gave the bright green dis- 

 charge, while a chain of iron gave the spur fire effect. 



The known transport of particles of the terminals from one pole to 

 the other, — the different effects of different intervening media on 

 induction as shown in Faraday's experiments, — the polar tension of 

 such media, &c. were instances of the train of molecular changes 

 consequent upon electrical action. 



Hitherto the polarity of the gaseous medium existing between the 

 metallic or conducting terminals of the electrical circuit was only 

 known as a physical polarity and not shown to have an analogous 

 chemical character with that existing in electrolytes anterior to elec- 

 trolysis ; but Mr. Grove stated that in a recent communication to 

 the Uoyal Society he had shown that mixtures of gases having oppo- 

 site electrical or chemical relations, such as oxygen and hydrogen, or 

 compound gases such as carbonic oxide, were electro-chemically 

 polarized or had their electro -negative and electro-positive elements 

 thrown in opposite directions : thus if a silvered plate be made posi- 

 tive, in such cases it is oxidized ; if negative, the dark spot of oxide 

 is reduced ; and an experiment was shown in which such a plate was 

 thus oxidized and the spot reduced in gaseous media. 



Here, as in the other experiments, was an effect on the terminals 

 and an effect of polarization of the intermedium. In the experiments 

 hitherto shown, solid terminals were used ; it became important to 

 examine what would be the effect of liquid terminals, for instance 

 water ; the spark or disruptive discharge of Franklinic electricity was 

 readily obtained from its surface, but hitherto no voltaic battery had 

 been found to show a discharge at any sensible distance from the sur- 

 face of water. 



Mr. Gassiot had procured to be constructed 500 cells of the nitric 

 acid battery, the combination discovered in 1S39 by Mr. Grove and 

 first shown at this Institution in the year 1840. The cells of this 

 battery were all well insulated by glass stems, and as regards inten- 

 sity of action it was probably far the most powerful ever seen. Mr. 

 Gassiot had kindly lent this apparatus for the illustration of this 

 evening's discourse, and by its aid Mr. Grove was able to show an 

 experiment which he had first made when experimenting with Mr. 

 Gassiot seme time ago, and which produced the effect he had long- 

 sought for, viz. a quantitative or voltaic discharge at a sensible di- 

 stance from the surface of water. The experiment was made as 

 follows : — a platinum plate forming the anode of the battery was 

 immersed in a capsule of distilled water, the temperature of which 

 was raised. A cathode or negative terminal of platinum wire was 

 now made to touch for a moment the surface of the water, and imme- 

 diately withdrawn to a distance of about a quarter of an inch ; the 



