ELECTRICAL PRINCIPLES OE THE ATLANTIC TELEGRAPH. 427 
with the ordinary apparatus less than half that speed was the 
utmost that could be attained.* 
There are, however, other methods by which, when all has 
been done that can be done by the improvement of instru- 
ments, the retardation and wearing-down of signals due to 
inductive action can be still further diminished. One of 
these, the method actually employed with the present Atlantic 
cables, affords such a beautiful example of the practical appli- 
cation of abstruse scientific principles, that we must briefly 
indicate its general features. The diagram (fig. 4) will facili- 
tate the explanation. Here B represents the battery; Gr a 
reflecting galvanometer ; C an electrical condenser (an arrange- 
ment equivalent to a very large Leyden jar) ; and R a conductor 
of very great resistance, forming a constant partial connection 
between the receiving end of the cable and the earth. The 
figure shows the sending end of the cable connected with the 
battery : under these circumstances a current enters the cable 
and charges both it and the condenser C, which is in permanent 
connection with it through the galvanometer, to an extent 
corresponding with its own electromotive force, and at the same 
time a slight current passes through R to the earth. These 
conditions are always maintained when no signals are being 
sent, but when the wire is required to be ready for their 
transmission. The galvanometer Gr, which shows a temporary 
deflection while the current is entering the condenser, returns 
to zero as soon as the condenser is fully charged. In order to 
send a signal, all that is necessary is to disconnect the sending’ 
end of the cable from the battery and connect it with the earth : 
this is done by pressing down the key c, the front end of which 
then comes in contact with a conductor, u, communicating with 
the earth, at the same instant that the other end, by rising, 
breaks the previously existing connection between the cable 
and the battery. On ceasing to press the key, the contact at' 
a is broken, and that at b restored; but the effect of moment- 
arily connecting the conductor of the cable with the earth is- 
to arrest, and even for an instant reverse, the flow of electricity 
.along it which is caused by the slight escape into the earth 
always taking place through R. The consequence is that- 
the electrical tension of the receiving end of the cable falls 
below that of the condenser C, and therefore electricity returns 
from the condenser into the cable, so as to equalise the tension 
in each, causing a deflection of the galvanometer as it passes. 
* It may be interesting to state that, according to Mr. Jenkin’s calculation, 
the speaking power of the two cables which are now in operation is from 
twice to three times as great as that of the cable of 1858, and we believe that 
this result is confirmed by experience of their actual working. 
VOL. V. NO. XXI. 2 G 
