ELECTRICAL PRINCIPLES OE THE ATLANTIC TELEGRAPH. 423 
The passage of a current through the instrument at the 
receiving station depends upon the existence of a difference of 
electrical tension between the earth and that end of the wire. 
If the electrical tension of the wire is greater than that of the 
earth, the direction of the current is from wire to earth; 
whereas, if the electrical tension of the wire is less than that 
of the earth, the current passes from earth to wire. The 
electrical tension of the wire can be increased, so as to become 
greater than that of the earth, by connecting the end at the 
sending station v r ith the positive pole of the battery ; and it can 
be diminished, so as to become less than that of the earth, by 
connecting the wire with the negative pole of the battery — it 
being understood in both cases that the second pole of the 
battery is connected with the earth. Now, if the conductor of 
the cable, instead of being surrounded by water, were sus- 
pended in the air, everywhere at a great distance from any 
conductor of electricity, in an immeasurably short space of 
time after one end was put in connexion with the battery its 
tension would be raised or lowered, throughout its whole 
length, to the full extent to which the particular battery em- 
ployed was capable of affecting it. The consequence would be 
that, on connecting the Yalentia end of the wire with the 
battery, a current of a certain definite strength would imme- 
diately show itself on the receiving instrument at Newfoundland 
— a current which would retain precisely the same strength as 
long as the connection with the battery was maintained, and 
would suddenly cease as soon as that connection was broken. 
Since, however, the conducting wire of the cable is far from 
being in the condition here supposed, the immersion of the 
cable in the sea making the conductor, as we have already said, 
equivalent to the inner coating of an immense Leyden jar, its 
electrical capacity is enormously increased beyond that of a 
similar wire suspended in the air ; or, what comes to the same 
thing, the quantity of electricity which must be put into it 
or removed from it in order to alter its electrical tension to 
the same extent is enormously greater. Hence, during the 
first instant after one end of the cable is connected with the 
positive pole of the battery, there is no perceptible increase of 
tension at the opposite end, and consequently no perceptible 
current. After a certain interval, the length of which depends 
upon the resistance of the conductor, the nature and thickness 
of the insulating coating, and the length of the cable, the 
current makes its appearance at the farther end, and for a time 
rapidly increases in strength, so that, after an additional in- 
terval of four times the length of that which preceded its first 
appearance, the current has attained about fifty-three per cent, 
of the strength of the strongest current which the particular 
