The telegraph manual: a complete history and description of the semaphoric, electric and magnetic telegraphs of Europe, Asia, Africa, and America, ancient and modern.

VELOCITY OF THE CURRENTS. 507
In charging the inner coating, nature furnishes simultaneously an opposite electricity on the exterior covering of the jar.
The glass intervenes in the use of the jar, and the gutta-percha
intervenes in the case of sub-marine cables. At the end c c,
the positive current is seen at rest, brought to the position by
the influence of the electricity of the earth, existing in the
water. This phenomenon is called the retardation of the current. If at A a negative current be applied, the positive in the
cable becomes neutralized. If the battery be disengaged from
the cable, and the end of the wire be allowed to hang in the
air for an hour, the electricity will be held in the cable in sufficient quantity to discharge a cannon, on renewing the earth
circuit. The current thus coming back is called the " return
current." The electricity of the earth encircling the cable is
negative, when it is charged with a positive current. If the
current transmitted through the cable was negative, then the
earth electricity would be positive, and the effect would be the
same. These imponderable elements seem to exist only in the
effort to unite one with the other.
It is this retardation of the electric current that renders the
succss of ocean telegraphy so exceedingly questionable.
I have, time and again, expressed a want of faith in the
practicability of operating long subaqueous conductors for telegraphic purposes, at least, until some new developments in
science dispels the difficulties hereinbefore mentioned. The
working of the subterranean telegraph lines in England, Denmark, Prussia, Russia, and other states of Europe, and of the
various submarine lines, in different parts of the world, prove
that long circuits through the water, or through the earth, can
not be successfully operated, and that the maximum circuit
that can be practically operated for telegraphic purposes, must
be less than one thousand miles.
ESTIMATED VELOCITY OF THE CURRENT.
The operating of the line from Sardinia through the Mediterranean Sea to Malta, and thence to Corfu, demonstrates the impracticability of working long submarine telegraphs. The time
required for the transmission of the electric current is irregular
and unreliable. Such are the facts as known at the present
time. The nearest estimate as to the time required for the
transmission of the electric current, can be reliably based upon
some experiments instituted by the brothers Bright, of England. The following was communicated to me by Mr. Bright:
" Answer 44th. In the course of a long series of experiments
carried on last year by my brother and myself, inquiries were