134 
ME. C. F. VABLEY ON POLARIZATION OF 
Thus, then, if the product of IxR remain constant, their ratio to one another may 
vary without varying the speed of the cable. 
The French Atlantic conductor consists of 400 lbs. to the nautical mile, and if made 
into a solid wire would in a length of 8T inches have the surface of 3^ square inches. 
The cable in round numbers is 2500 nautical miles long, and this length has a capa- 
city of 1000 microfarads, the same as 3^ square inches of platinum surface in water at 
a potential of ‘6 or *7 volt. 
1 = 34 inches, 11 = 2500 miles; by varying these until I = R in length (their product 
remaining constant), we get the length in round numbers of rather less than 1100 yards 
(or, say, half a mile) as that at which the bare wire if coated with platinum would equal 
in speed the cable now working from France to St. Pierre, the longest cable in the 
world. 
As the surface of the wire increases with its diameter, and its conducting-power with 
the square of the diameter, the speed of transmission through a bare wire varies only 
as its diameter and not as its mass ; therefore a bare solid conductor capable of working 
ten words a minute through 2500 miles of ocean must be more than 250,000 feet in 
diameter to have the same speed as the present French Atlantic Cable. 
This mode of telegraphing is only practically available within distances of less than 
a mile, and this explains why Lord Dudley’s uninsulated cable between Dover and 
Calais would not work. The distance being 20 miles (40x^ m iles) and the conductor 
about half the diameter of the French Atlantic (which gives on an average ten words a 
minute in actual practice), the speed would be fjup X^=l word of five letters in 320 
minutes =1 letter of three signals in 53 minutes =1 simple signal in 18 minutes. 
The measures in the Tables of the capacity of the platinum surfaces in the water are 
only approximately true. 
There is considerable difficulty in these experiments, owing to the discharge not being 
sensibly instantaneous, and the absorption being very large. 
The general truth that the capacity increases when the potential increases is, however, 
beyond all manner of doubt established. 
This is the very reverse of what was expected by the author when he commenced the 
investigation. 
