which connect Light with Electricity. 255 



ten minutes in the camera ; it was very beautiful. Immediately 

 afterwards, a second was made by submitting the iodized 

 plate to the intense current of a pile of twenty elements* du- 

 ring the entire continuance of the action of light upon it. 



After the lapse of fourteen minutes, which were judged ne- 

 cessary because the sky had become overcast, the Daguer- 

 reotyped drawing was found without fault, without any stria- 

 tion, or anything indicating that the current had acted in the 

 direction of the line connecting the points of contact of the 

 conductors, or in a direction parallel, oblique or perpendicu- 

 lar to itf. 



Thus an iodized leaf of silver plate is not altered in its che- 

 mical nature by the passage of a strong voltaic current; the 

 iodine is not volatilized, and the iodide remains quite as sen- 

 sible to the action of light as before. 



Inversely, I asked myself what influence does light exert 

 upon an action due to electricity. In order to ascertain this, 

 I placed a voltameter J in a voltaic circuit of ten pairs of the 

 pile above described, and I estimated the quantities of gas ob- 

 tained in equal times measured by an excellent seconds pen- 

 dulum by Ferdinand Berthoud. These quantities were inva- 

 riable, whether the instrument was in the most complete dark- 

 ness or exposed to a large beam of light reflected by the helio- 

 stat, or lastly, when it was placed in the different rays, coloured 

 or dark, of a spectrum, obtained by projecting a ray of light 



* This constant battery is constructed on Daniell's plan. It is formed 

 of cylindrical pairs, the common height of which is m, 149, and their dia- 

 meter for the coppers m, 06, and for the zincs m, 045. The coppers plunge 

 into (bocaux) wide-mouthed glass bottles filled with a concentratedjsolution 

 of sulphate of copper; the zincs, amalgamated hot, are immersed in a so- 

 lution of chloride of sodium contained in animal membranes. The pairs 

 communicate with each other by means of very thick copper wires which 

 are soldered to them on one side, and which dip on the other into reser- 

 voirs full of mercury, adapted to the edges of the case in which the 

 wide-mouthed bottles are placed. This pile readily preserves in a state of 

 incandescence an iron wire m- 0005 in diameter, and more than m, 3 in 

 length ; by the contact of charcoal cones it gives a luminous point, the 

 brightness of which the eye cannot support, volatilizes between them a 

 thin brass wire, and disengages from 75 to 80 cubic centimetres of gas in 

 a minute by decomposing acidulated water. 



f This experiment was made on the 29th of May, 1841, with the assist- 

 ance of my friend Professor Secretan-Mercier, who was so kind as to lend 

 me his instrument and his skill in using it. It is therefore anterior to the 

 communications of M. Arago on the accelerating processes of M.Daguerre, 

 inserted in the Comptes Rendus for the 28th of June and the 5th of July. 



X This voltameter is formed of two laminae of platina m- 03 in length 

 by m, 01 broad, communicating with two wires of pure copper annealed 

 m, 003 in diameter, and m, 441 long. The electrolyte was a mixture of 

 seven parts pure water with one of concentrated sulphuric acid. The 

 gases were collected over water in a graduated test-tube. 



