After the close of the session of Congress in the spring, 1844, a
series of experiments were commenced by the request of Prof. Morse,
under the direction of Mr. Vail, for the purpose of ascertaining what
amount of battery was absolutely required for the practical operation
of the telegraph. From the first commencement of its operations to the
close of the session, so anxious were the public to witness its almost
magic performances, that time could not be taken to put it in a state
to test either the size of the battery required, or bring into use all
the machinery of the register. On that account, but _one wire_ was used
during that period for transmitting and receiving intelligence, and
the capabilities of the instrument were shown to some disadvantage;
requiring the constant attendance of those having charge of the two
termini.
This first experiment made was to ascertain the number of cups
absolutely required for operating the telegraph. Eighty cups had been
the number in use. Upon experiment, it was found, that two cups would
operate the telegraph from Washington to Baltimore. This success was
more than had been anticipated and urged on further experiments, which
eventually proved that the earth itself furnished sufficient galvanic
power to operate the electro magnet without the aid of a battery.
In the first experiment, a copper plate was buried in the ground,
and about three hundred yards from it, a zinc plate was also buried
in the ground. To each of these plates a wire was soldered, and the
ends brought into the telegraph office, and properly connected with
the key and electro magnet of the register. The battery not being in
connection. Upon manipulating at the key, it was found that the electro
magnet was operated upon and the pen of the register recorded. This led
to another experiment upon a more magnificent scale, and nothing less
than that of using the copper plate at Washington, and the zinc plate
at Baltimore, with the single wire, connecting those distant points,
and the battery thrown out. Here, too, success followed the experiment,
though with diminished effect. By the application of a more delicate
apparatus the _Electro Magnet_[9] was operated upon, and the pen of the
_registering instrument recorded_ its success. From these experiments,
the fact appears conclusive, that the ground can, through the agency of
metallic plates, constantly generate the galvanic fluid.
[9] Franklin appears to have been the first, or among the first, who
used the ground as part of a conducting circuit in the performance
of electrical experiments. Steinheil it appears was the first to use
the ground as a conductor for magneto electricity. Bain, in 1840, was
the first to use the ground as a source of electricity in conjunction
with its conducting power, as a circuit. Prof. Morse, has since the
establishment of the telegraphic line, used the ground as half the
line, with perfect success, employing the battery; and Mr. Vail, in an
experiment in 1844, succeeded in operating the electro magnet, with its
armature attached to a lever, without any battery.
_Six Independent Circuits, with six wires, each wire making an
independent line of communication._
[Illustration: FIG. 23.]
In the above figure, 23, let the right hand side represent Washington,
and the left, Baltimore. The lines marked 1, 2, 3, 4, 5, and 6, between
_m_ and _k_, respectively, represent the six wires connecting (for
example) Washington with Baltimore. Each cluster of black dots, P and
N, represent the batteries of that line upon which it is placed. There
are three batteries at W, and three at B; _m_ 1, _m_ 3, and _m_ 5,
represent the three magnets, or registers, and _k_ 2, _k_ 4, and _k_ 6,
the three keys, or correspondents, at Baltimore; _k_ 1, _k_ 3, and _k_
5, are the three keys, or correspondents, and _m_ 2, _m_ 4, and _m_ 6,
the three magnets, or registers, at Washington. C B is the copper plate
at Baltimore, and C W, the copper plate at Washington, one at each
terminus.
In order to operate the six lines, simultaneously, if required by the
pressure of telegraphic communications, there must be three operators
at each station, commanding their respective keys, and presiding at
their respective registers. If the three operators at Washington choose
to write in Baltimore, together, or in succession, on their respective
registers at the latter place, the galvanic current of the three lines
1, 3, and 5, takes this direction. Commencing at the point, P, of the
three batteries, 1, 3, and 5, at W, it passes to _k_, of the keys;
thence along the wires to _m_, the magnets, 1, 3, and 5 at B; thence
to the single wire, where the three currents join in one to C B, the
copper plate; then through the ground to C W, the other copper plate;
then up the single line to their respective batteries at the point, N,
having each finished its circuit independently of each other.
If, in reply, the three operators at Baltimore wish to write upon
their registers at Washington, either together, or in any succession,
they may choose; the fluid leaves the point, P, of their respective
batteries, at Baltimore, 2, 4, and 6; unite in the single wire to C
B, the copper plate; then pass through the ground in the direction
of arrows to C W, copper plate at Washington, then along the single
wire to their respective magnets, _m_, 2, 4, and 6; then along the
extended wires to _k_, 2, 4, and 6 at Baltimore; and then to N pole of
their respective batteries. In this manner six distinct circuits may
be operated independently of each other, at the same time, or in any
succession, with only one wire for each, and the ground in common, as a
part of the circuit.
It is obvious from the above arrangement that if one wire only,
extended between two distant points, will suffice to enable
communications to be exchanged with each other; that any number of
wires extended, will also, each, individually, give a distinct and
separate line for telegraphic purposes, independently of all the other
lines on the same route.
[Illustration: FIG. 24]
In figure 24, the same arrangement of wires is observed as respects
their number, and the situation of the keys and magnets; but, with this
difference, that instead of six batteries, one for each wire, there is
but one, which is placed upon the single wire, with which the six wires
join. The battery is represented by four black dots, marked N B P. The
course of the fluid in this case is from P to C, the copper plate on
the left side; then through the ground to C, the copper plate on the
right; then through the single wire to any of the six wires, which may
be required, then to the single wire on the left side to N, of the
battery. It is obvious that in this arrangement there is a division of
the power of the battery, depending upon the number of circuits that
may be closed at any one instant. For example: if circuit 1 is alone
being used, then it is worked with the whole force of the battery. If
1 and 2 are used at the same instant; each of them employ one-half the
force of the battery. If 1, 2 and 3 are used, then each use one-third
its power. If 1, 2, 3 and 4, then each circuit has one-fourth the
power; if 1, 2, 3, 4 and 5 are used, at the same moment, then one-fifth
is only appropriated to each circuit, and if 1, 2, 3, 4, 5 and 6, then
each employ a sixth part of the galvanic fluid generated by the battery.