III. On the luminous discharge of voltaic batteries, when examined in carbonic acid vacua

On the 24th of May, 1859 (Proceedings, May 26, 1859), I communicated 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 previously 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 is 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, ½ 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.