ATLANTIC TELEGEAPHY. 
547 
currents of electricity in succession. The effect of this is 
to absorb the preceding* wave^ and to neutralize it much 
more quickly than would be the case if the wire were 
left to discharge itself in the usual way. In a suspended 
wire_, as there is but little induction_, there can be no accumu- 
lation of static charge worth noticing ; whereas a submarine 
wire^ unless attention be paid to this_, becomes useless for 
telegraphy. These remarks will serve to explain the reason 
why the telegraphic signals through the long line of the 
Atlantic telegraph will be so slowly delivered. The conditions 
are now well understood^ and no doubt increased rapidity will 
be given to the rate of charging and discharging this vast 
length of wire_, when it is laid again in the depths of the sea. 
The delicacy which has already been given to the instruments 
employed wiU be appreciated. The Atlantic Telegraph Com- 
pany possess instruments which are capable of being rendered 
active^ by the feeble current set up by the saliva of the mouthy 
acting on a sixpence and a piece of zinc_, through a circuit of 
500 miles^ and record by a definite amount of attraction. 
It is difficult to conceive any instrument intended for practical 
use having a higher degree of delicacy than this. It is scarcely 
necessary to repeat^ yeC desiring to make the conditions of an 
Atlantic cable perfectly intelligible to all^ it is thought advisable 
to do so. The earth is a reservoir of electricity and the wire 
which is laid over the deep-sea bed is also charged with this mys- 
terious agent. When the earth and the wire are in the same 
state^ there would be no indication in any instrument with which 
they may be connected. The balance remains undisturbed^ 
the magnetic needle is at rest } but^ produce the slightest 
motion in one^ which is not produced in the other_, and the 
needle gives a signal. This is the principle governing the 
electric band^ and of course every arrangement is made so as 
to ensure the utmost degree of sensitiveness. 
The electric conductor of the Atlantic cable is formed of 
seven wires (figs. 4 and 8_, PI. XXI. )_, six around one. Seven 
wires are used rather than one (see Plate) to give greater 
freedom to the electricity^ in passing by presenting a' more 
extensive surface to it. There are mechanical reasons also 
why a band of wires is preferable to one wire. The most 
serious accident that can happen to a submerged wire is 
its severance. Copper wier cannot always be depended 
upon to present the same amount of strength in every part. 
It frequently happens that an inch_, or even a less portion of 
a wire,, is crystalhne^ and therefore liable to break in being 
coiled. By using seven sections instead of one,, the pro- 
bability of a fatal breach of continuity is greatly reduced. 
It is scarcely to be expected that seven weak places would 
