10* Mr. J. P. Joule on the Electric Origin 



was placed on the top of the receiver. A copper wire, fast- 

 ened to the ring of the sliding rod, connected the platinized 

 silver with the galvanometer. 



26. The sliding rod was now moved until tlie platinized 

 silver in connexion with it was immersed in the acidulated 

 water. Then the pump was worked until a very excellent va- 

 cuum was obtained, and so tight was every part of the appa- 

 ratus that it could be left alone for half an hour without the 

 admission of any appreciable quantity of air. The galvano- 

 meter indicated a permanent deflection* of 27°. I now placed 

 a piece of glass so as to prevent the needle from going lower 

 than 27°, and by means of the sliding rod I removed the pla- 

 tinized silver entirely out of the acid. After it had been ex- 

 posed during a quarter of an hour I re-immersed it, when the 

 needle sprang from 27° to 30° and back, indicating a trans- 

 itox'y deflection of about 28|°. Although the effect of immer- 

 sion exhibited by this experiment is extremely small, it ap- 

 peared to be almost entirely occasioned by the repose of the 

 electric condition of the iron, for when, instead of entirely 

 withdrawing the platinized silver, its extremity was just al- 

 lowed to touch the liquid, the transitory deflection was only 

 27i° after an exposure during a quarter of an hour. 



27. On admitting a quantity of air into the receiver suffi- 

 cient to counterbalance the pressure of one inch of mercury, 

 the effects of immersion were considerable after a very short 

 exposure of the platinized silver. In a quarter of an hour it 

 collected upon its surface sufficient oxygen to cause the needle 

 to spring from 27° to 78°, whether it had or had not remained 

 in contact with the liquid during its exposure. 



28. When, instead of the vacuum, 1 used an atmosphere of 

 hydrogen, the exposure of the platinized silver for any length 

 of time did not render the current more intense at the mo- 

 ment of immersion than it remained permanently. And even 

 when the hydrogen was diluted with one (|uarter of its bulk 

 of atmospheric air the transitory ellectsdidnot appear, on ac- 

 count, no doubt, of the unionf of the oxygen with the hydro- 

 gen as fast as the former, or both, collected upon the plate. On 

 using a mixture of equal bulks of hydrogen and air, the transi- 

 tory eflects were very small, even alter the platinized silver 

 had been exposed for ten minutes. 



29. I made several experiments with carbonic acid, but the 



=^ No change in the permanent deflection of the needle was occasioned 

 by the removal of atmospheric pressure. 



t The phenomenon of Dcebereiner, so fully investigated by Faraday, 

 to whose paper, published in the Phil. Trans, for 1834, I refer the reader 

 for some valuable observations on the power possessed by metals of con- 

 densing gases upon their surfaces. 



