480 Mr. Grove on some Phenomena of 



brilliant voltaic arc, while in hydrogen or a vacuum with the 

 same power a feeble spark only is perceptible at the moment 

 of disruption. Mercury on the other hand gives a tolerably 

 brilliant spark in hydrogen, azote, or a vacuum, and one more 

 nearly approaching to that which it gives in air. Thus in an 

 oxidating medium there are three requisites for a brilliant 

 discharge, viz. oxidability, volatility, and looseness of ag- 

 gregation : in other media the two latter alone obtain; and the 

 brilliant arc given by charcoal appears to depend principally 

 upon the last ; thus wood charcoal gives a larger and more 

 diffuse flame than the carbon from gas retorts. 



In the following list the metals are arranged, as nearly as 

 may be, in respect to the length and brilliancy of the arc 

 they give in atmospheric air, the discharge being taken be- 

 tween two points of the same metal : 



Potassium, Antimony, 



Sodium, Bismuth, 



Zinc, Copper, 



Mercury, Silver, 



Iron, Gold, 



Tin, Platinum. 



Lead, 

 It has been noticed by Sir H. Davy, Dr. Hare, and Mr. 

 Daniell, that a certain portion of matter is projected from the 

 positive to the negative electrode : the quantity thus percepti- 

 bly projected is indeed very small ; but I observed that when 

 the discharge was taken in a close vessel the whole interior 

 was lined with a pulverulent deposit, which if the vessel con- 

 tained atmospheric air was an oxide of the metal employed, 

 but if it contained azote or hydrogen was a reguline preci- 

 pitate of the metal. Faraday's researches have established, 

 that in electrolysis a voltaic current can only pass by a de- 

 rangement of the molecules of matter; that the quantity of 

 the current* which passes, is directly proportional to the 

 atomic disturbance it occasions : he deduces from this that 

 the quantity of electricity united with the atoms of bodies 

 is as their equivalent numbers, or in other words, that the 

 equivalent numbers of different bodies serve as the exponents 

 of the comparative quantities of electricity associated with 

 them. Now what takes-place in the disruptive discharge? 

 When we see the dazzlino- flame between the terminals of a 

 voltaic battery, do we see electricity, or do we not rather see 

 matter, detached, as Davy supposed, by the mysterious agency 



* However unpredicable the words quantity, current, &c. may be of an 

 agent imponderable, and having no definite relation to space, these words 

 express understood functions, and it seems impossible to devise others 

 which would npt be open to gimilar objections. 



