1823.] Royal Society. 303 



A series of microscopical drawings by Messrs. Bauer and 

 Clift illustrated the details in this paper. 



March 6. — On a new Phenomenon of Electromagnetism, by 

 SirH. Davy, Bart. PRS. 



The experiment described in this paper had been first made 

 by the author about fifteen months ago ; but had been repeated 

 by him, very recently, through the kindness of Mr. Pepys, with 

 a battery consisting of two plates, each containing 100 square 

 feet, which had been constructed, under the direction of that 

 gentleman, for the London Institution ; and of which, Sir Hum- 

 phry hoped, Mr. Pepys would communicate a description to the 

 Society. The experiment, however, might be made with a pair 

 of plates each containing three or four square feet only. 



Sir Humphry had conceived, immediately after the publica- 

 tion of Mr. Faraday's ingenious experiments on electromagnetic 

 rotation, that if mercury could be made to revolve by electro- 

 magnetism, some new light might be thrown upon the subject, 

 as the motions of that substance could not be affected by the 

 disadvantages attending mechanical suspension. On immers- 

 ing, accordingly, the two wires of a battery in mercury, and 

 presenting a magnet to them, either above or below, the 

 mercury was made to revolve around the wires. From the 

 appearance of the motion, Sir Humphry was induced to be- 

 lieve that it could not be owing to any simple action, but 

 that it must be the result of a composition of forces ; and that 

 some kind of motion would be produced in mercury by the 

 agency of electricity alone. In order to determine this, he 

 covered the surface of the mercury with weak acids, and with 

 finely divided matter, as the seed of lycopodium, the white 

 oxide of mercury, &c. ; but no distinct effects could be observed. 

 It then occurred to him, that, from the circumstances of this 

 experiment, the motion, if any took place, must be chiefly con- 

 fined to the lower surface of the mercury ; and he therefore 

 reversed it. Two copper wires, one-sixth of an inch in diame- 

 ter, and carefully polished at their extremities, were passed, per- 

 pendicularly, through the bottom of a glass basin, and made 

 non-conductors by wax, except at their extremities. Mercury 

 was then poured in, to the height cf one-tenth of an inch above 

 the wires, and, upon connecting them with the battery, it was 

 thrown into violent motion, being raised, over the wires, into 

 conical elevations of one-tenth or one-twelfth of an inch, from 

 which waves flowed in all directions. Upon bringing a magnet 

 over the wires, the conical eminences were depressed, the circu- 

 lar motion ceased, and currents were produced in the mercury 

 in opposite directions ; and, upon its nearer approach, the emi- 

 nences were converted into vortical depressions. 



That the motion given to the mercury by the agency of elec- 

 tricity, as just described, did not arise from the heat produced, 

 was experimentally determined ; when the large battery was 



