540 Boyal Society : — 



is precisely analogous therefore to the line D, which is stopped by an 

 alcohol flame into which salt has been put. Should, however, the 

 ruby glass be of a much higher temperature than the coals behind it, 

 the" greenish light which it radiates overpowers the red which it 

 transmits, so that the light which reaches the eye is green more than 

 red. This is precisely analogous to what is observed when a Bunsen's 

 gas-lamp with a little salt is placed before the Drummond light, when 

 the line D is no longer dark but bright. 



In fact, the law, " the absorption of a particle is equal to its radia- 

 tion, and that for every kind of light," only applies to the case where 

 the temperature of the particle is equal to that of the source of the 

 light which passes through the particle. If the temperature of the 

 source of light be greater, one quality of light will predominate ; if, 

 on the other hand, the temperature of the particle be greater, another 

 quality of light will predominate. 



" On the Luminous Discharge of Voltaic Batteries, when examined 

 in Carbonic Acid Vacua." By J. P. Gassiot, Esq., F.R.S. 



On the 24th of May, 1859 (Proceedings, May 26, 1859), I com- 

 municated to the Royal Society a short notice of my having obtained 

 the stratified discharge from a voltaic battery of 3520 elements 

 charged with rain-water ; and also with one of 400 elements charged 

 with nitric and sulphuric acids, each cell of both batteries being 

 insulated. I stated also that with the latter (as I had previ- 

 ously shown with the former), spark discharges passed between two 

 terminal copper plates through the air, before the completion of the 

 circuit. 



The well-known luminous arc in air, as usually obtained from 

 an extended series of the nitric-acid battery, was very brilliant, but 

 from the small size of the porous cells (3 inches long, \ inch broad) 

 containing the nitric acid, it was only tried by a momentary action. 

 With the water-battery I have never been able to obtain a continuous 

 discharge in air similar to the voltaic arc ; whether from points or 

 plates, the discharges from this battery are invariably in the form of 

 minute, clearly defined, and separated sparks. 



Although the water-battery consisted of nearly nine times as many 

 metallic elements as the nitric-acid battery, it exhibited by the gold- 

 leaf electroscope very little increased signs of tension. 



This is in accordance with the results obtained by me in 1 844, when 

 I showed that the tension of a single cell increased in force according 

 to the chemical energy of the exciting liquid. " In all the experi- 

 ments I made, the higher the chemical affinities of the elements used, 

 the greater was the development of evidence of tension" (Philosophical 

 Transactions, 1844, part 1. p. 52). 



Recently, through the kind introduction of Professor Wheatstone, 

 I have had an opportunity of experimenting with 512 series of 

 Daniell's constant battery ; and my present object is to present to the 

 Royal Society a short account of the results I have obtained, and to 

 describe the appearance and character of the voltaic discharge of 

 these several batteries when taken in vacua. 



