M. Matteucci on the Electric Discharge of the Jar. 35 



kept in the dark, the other was exposed to good sunshine. In 

 both instances the hberated iodine gave an intense yellow to 

 the solution, and in both cases the quantity of metallic silver 

 deposited was precisely the same. 



This yellow fluid being analysed by the prism was found to 

 obstruct all the rays above the green, whilst it permitted the 

 permeation of the yellow and orange rays in great quantity 

 and power. It is therefore evident that the luminous rays of 

 the solar spectrum have no power in retarding electro-che- 

 mical action. 



I submit these details of experiments in a new and im- 

 portant branch of science to the Chemical Society, knowing 

 that they form but a very imperfect account of an extensive 

 series of phaenomena, but I do so with the hope of being en- 

 abled eventually to render my contributions more comprehen- 

 sive. 



Vlli. Experiments on the Electric Discharge of the Jar. [Ex- 

 tract of a letter from M. Matteucci to M. Arago.)* 



HAVING lately had occasion, in one of my lectures on 

 electricity, to employ the new electrical machine of 

 Armstrong, I thought it would be interesting to repeat the ex- 

 periments of Colladon with this machine. The large quantity of 

 electricity which is developed with this machine led me to hope 

 that, even with an ordinary galvanometer, we might obtain in- 

 dications of current by making a communication between the 

 insulated boiler and the conductor furnished with points and 

 also insulated, agaiyist 'which the jet of vapour is directed. It 

 was, indeed, with an ordinary galvanometer, the wire of which, 

 makes 200 turns, and which is furnished with a somewhat im- 

 perfect static arrangement, that I obtained, operating in the 

 manner I have stated, a fixed deviation in the direction given 

 by the conditions of the experiment. This direction took 

 place the contrary way, on reversing the position of the ex- 

 tremities of the galvanometer, being always directed from the 

 extremity of the wire turned toward the vapour to that of the 

 boiler. I have tried some experiments with a view of com- 

 paring the intensity of the current with the tension of the vapour 

 in the boiler ; and I have operated from two atmospheres up 

 to five successively. The fixed deviation increased from 3 de- 

 grees up to 10 and '27 degrees, going from the pressure of 

 t\vo atmospheres to four. It appeared to me that the devia- 

 tion was sensibly the same for pressures exceeding four at- 

 mospheres. On holding one of the extremities of the wire 

 * From the Comptes Hendm, April 14, 1845, 



D2 



