244 



Mr. C. F. Varley on Polarization of 



[Jan. 12, 



of the funnel, some bubbles of hydrogen gas appear just as the last of the 

 mercury is running out, the decrease of surface evidently augmenting 

 the potential sufficiently to decompose the water : floating a small piece of 

 platinum on the mercury renders this phenomenon much more distinct. 



All attempts to polarize the mercury with oxygen have failed to give a 

 current. By depolarizing the mercury with a battery until no current is 

 generated by varying the dimensions of the exposed mercury surface, a me- 

 tallic surface neutral to the fluid is obtained. 



The second part of the paper refers to the electrostatic capacity of plati- 

 num plates in dilute acid and water. 



In order to determine this point, it is necessary to use sensitive, rapidly 

 oscillating, reflecting galvanometers of very small resistance. The author 

 has succeeded in measuring the charge which a square inch of platinum ex- 

 posed to another square inch of platinum surface receives from potentials 

 varying from 0*02 of a DanielPs cell up to 1*6 Daniell's cell. From a po- 

 tential of "02 to 08 the capacity remains sensibly constant; that is, 

 the discharge from the plates varies directly as the potential. When the 

 potential increases beyond 0*08, the charge which the plates receive in- 

 creases in a greater ratio, the capacity being 3*3 (in one experiment) 

 and 3'1 (in another experiment) times as great with a potential of 1*6 

 as it was with the potential of 0*1. 



There is great difficulty attending accurate determination of the latter 

 amounts ; but the author expects that this increase of capacity will be 

 found to vary as the square root of the potential. The capacity of the 

 platinum plates with varying powers is shown in the accompanying Tables. 



The author thinks these experiments tend to show that the fluid does 

 not actually touch the platinum plate, but is separated from it by a film, 

 which film, if a pure gas, must be less than the x 000 q 0Q 000 part of an inch, 

 when very small potentials are used. This distance decreases as the poten- 

 tial rises. Inasmuch as two surfaces equally electrified with the opposite 

 electricities attract each other with a power varying inversely as the square 

 of the distance, the experiment would seem to indicate that at very small 

 distances the platinum repels the water with a power varying inversely as 

 the cube of the distance. 



The phenomena of electrification render accurate determinations of the 

 capacity extremely difficult. The fact of the phenomena of electrification 

 being present, leads the author to think that the separating film (if 

 such a film exists) is not a pure gas, but has five or more times as much 

 electrostatic capacity as pure gas. 



A useful inference drawn from the above experiments is the impossibility 

 of working through any considerable length of uninsulated wire in the ocean. 



The French Atlantic cable from Brest to St. Pierre works, upon the 

 average, tea words per minute ; the author calculates that a solid con- 

 ductor of the same weight per mile as that used between the above stations 

 must be reduced to a length of less than 1 100 yards in order that the rate 

 of signalling through it shall be not slower than through 2500 miles of 



