Fig. 2. 



between Mercury Surfaces. 485 



tion is of very short duration. The mirror-like brilliancy of a 

 mercurial surface is no criterion that the whole of the visible 

 molecules may not be suboxide ; for the reflection would not 

 be lessened until the formation of this suboxide became suffi- 

 cient to impair the smoothness of the surface. And the cur- 

 rents measured between the disturbed and quiescent surfaces 

 of mercury are probably currents set up between surfaces in 

 different states of oxidation, the less oxidized of the two being 

 positive to the other. 



To put this more fully to the test of experiment, an appa- 

 ratus was made up very much on the principle of that used by 

 Mr. Varley for producing currents by mercury when polarized 

 w T ith hydrogen. The object in view was, that one of the sur- 

 faces of mercury might 

 be expanded or con- 

 tracted at pleasure to 

 either condense or break 

 the supposed film of 

 suboxide. The funnel- 

 shaped vessel / (fig. 2) 

 was connected with a 

 reservoir of mercury, a, 

 in such a way that, by 

 increasing or decreasing 

 the pneumatic pressure in 

 «, the mercury in/ would 

 rise or fall. This vessel was immersed in a deep trough con- 

 taining distilled water. The surface of the mercury in/formed 

 one side of a galvanic couple, with a quiescent surface of mer- 

 cury contained in the bent-up end of a thistle-tube b for its 

 other side. When the mercmy-niveau was down in the 

 shank of the funnel, whatever suboxide might be upon it 

 would be split up when the mercury was raised suddenly 

 in the funnel. When contracted at the bottom of the funnel, 

 the diameter of the mercury face was about 0*6 centim. ; 

 when raised and expanded, it was between 2 and 2'5 centims., 

 the area being therefore 10 to 15 times as great. 



When the temperature of the whole had become uniform, a 

 very slight current was observed on the galvanometer con- 

 nected between protected wires dipping into the two masses 

 of mercury. The mercury was then drawn steadily down 

 into the shank of the funnel, and a considerable deflection 

 towards the right observed, showing a diminished electro- 

 positiveness. When the needle became still, the mercury 

 was allowed to return to its former level ; and an excursion 

 to the left was noted. When the needle was again steady, 



