﻿312 Royal Society : — Mr. C. F. Varley on the Polarization 



current is generated by varying the dimensions of the exposed mercury 

 surface, a metallic surface neutral to the fluid is obtained. 



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

 platinum 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 exposed to another square inch of platinum surface 

 receives from potentials varying from 0*02 of a Darnell's cell up to 

 1*6 Daniell's cell. From a potential of 0*02 to 0'08 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 increases 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 y 000 ^ 00Q 

 part of an inch, when very small potentials are used. This distance 

 decreases as the potential 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 se- 

 parating 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 im- 

 possibility 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, ten words per minute; the author calculates that a 

 solid conductor of the same weight per mile as that used between the 

 above stations must be reduced to a length of less than 1100 yards in 

 order that the rate of signalling through it shall be not slower than 

 through 2500 miles of the same conductor insulated ; and the bare 

 wires can only be practically worked on circuits not exceeding a mile. 



