IMPROVEMENTS IN ELECTRIC TELEGRAPHS
Year: 1876

page_text: “LETTERS PATENT to John Muirhead, junior, of Stanley Villa, Thornton Hill,
Wimbledon, in the County of Surrey, for the Invention of "IMPROVEMENTS IN
ELECTRIC TELEGRAPHS." Partly a communication from abroad by Alexander
Muirhead. residing at Aden.
Sealed the 30th September 1876, and dated the 21st June 187
PROVISIONAL SPECIFICATION left by the said John Muirhead at the Office
of the Commissioners of Patents on the 21st June 1876.
JOHN MUIRHEAD, junior, of Stanley Villa, Thornton Hill, Wimbledon, in the
County of Surrey. "IMPROVEMENTS IN ELECTRIC TELEGRAPHS." Partly a com-
munication from abroad by Alexander Muirhead, residing at Aden.
The Invention consists in improvements in the methods of working duplex
telegraphy, especially on submarine cables, in conjunction with compensating
circuits, whereby any want of perfect electric similarity between the cable and
artificial line can be compensated for or corrected, and also a gain of speed in
signalling obtained.
In ordinary working of submariné telegraph lines of any considerable length it
is usual to employ condensers either in the sending or receiving circuits, or in both.
In duplex working I use condensers sometimes placed between the battery key and
the junctions of the branches of a Wheatstone bridge, as shown in Figure 1.
Sometimes I use two condensers or sets of condensers, as in Figure 2, one set
being placed between the end of one branch of the bridge and the cable, and the
other set between the other banch of the bridge and the artificial line or com-
pensating circuit. By this latter arrangement (which I shall call that of bridge
condensers), it is found that the arms of the bridge may be greatly reduced in
resistance, and a consequent reduction in the retardation of the signals effected.
The terminals of the receiving instrument may be connected on the line side of the
cor. densers with the cable and artificial line respectively, as shown at a, b, Figure 2,
or the receiving instrument may be connected with the oppoüte poles of the con-
densers on the bridge side, as shown by the dotted lines m, n, in the same Figure.
I prefer the latter arrangement.
I also employ condensers in circuit with the receiving instrument,-
1st. Connected in the same manner as an ordinary shunt with the terminals of
the instrument, as at a, Figure 3.

page_text: 2ndly. Or so connected that the condenser intervenes between one pole or
terminal of the receiving instrument and the junction of the cable, or the artificial
line with the arm of the bridge or with the bridge condensers, as at b, Figure 3.
I sometimes use both arrangements in combination.
In some cases where there is a difficulty in obtaining a perfect balance I employ 5
an arrangement of conductors which I call a "double" bridge. To the ends of the
branches of the ordinary bridge remote from their junction with one another I
attach a conductor of adjustable resistance, an intermediate point of which I connect
either to earth, Figure 4, or to the junction of the bridge branches with one another
directly or through a resistance coil, as in Figure 5, and with or without condensers
as circumstances may require.
I find it sometimes convenient as a means of perfecting the balance to make use
of an electro-magnetic adjustment either alone or in conjunction with some of the
adjustments above described. I insert the primary of an electro-magnetic coil with
moveable soft iron core between the sending key and the junction of the branches
of the bridge, the secondary (the resistance of which is adjustable) being connected
in one of the following manners :-
1st. Its ends are connected with the poles of the receiving instrument in the
manner of a shunt, as shown in Figure 6.1
2nd. Or its ends are connected with those of the branches of the bridge, as a
shown in Figure 7.
3rd. Or one of its ends is connected with one pole of the receiving instrument
and the other end with the junction of the cable or artificial line with its arm of
the bridge or bridge condensers, as shown in Figure 8.
4th. Or the secondary wire in parallel circuit with a suitable resistance coil is
used as one branch of the bridge itself, as in Figure 9.
I also sometimes insert the primary wire between the cable and one branch of
the bridge, whilst the secondary is inserted between the artificial line and the other
branch of the bridge, or vice versa, the requisite adjustment being effected by
placing resistance coils in parallel circuit with either wire as a shunt. This arrange-
ment is shown at Figure 10.
Another method of adjustment by which a balance is sometimes facilitated
consists in the addition of resistance coils between the earth terminals of any or all
the consecutive sections of the artificial line; or between the last earth terminal
and the earth itself. This has the effect of slightly increasing the retardation of
the artificial line. On the other hand should it be desirable to diminish the
retardation I effect this by placing a coil of suitable high resistance between the
line terminals so as to be in parallel circuit with that part of the line whose
retardation is too great.
Instead of using ordinary resistance coils to form the branches of the bridge I
sometimes use two appropriate sections of artificial line.
As a means of removing disturbances that sometimes occur in the balance I have
found the arrangement shown at Figure 11 effective. It consists of inserting small
resistances between the sets of "bridge condensers" and the cable and the
artificial line respectively. Either or both these resistances should be abjustable.
- Another method consists in placing these resistances between the junctions of
the bridge with the receiving instrument and the "bridge condensers" last referred
This arrangement is shown at Figure 12.
to.
As an additional means of eliminating the disturbances of the balance I some-
times employ a condenser of small capacity, one of whose poles is connected to
earth, the other pole being connected to one branch of the bridge at a point best
ascertained by trial. This is shown at y in Figure 12.
Sometimes in my method of working with bridge condensers I also employ an
arrangement of a condenser and ahigh resistance coil, as shown at Figure 13. One
pole of the condenser is connectedthrough a high resistance to the end of one of the
branches of the bridge, the other pole being connected to earth.
All the above arrangements with the slight modification which will be evident

page_text: to electricians are equally applicable to the working with a differential receiving
instrument instead of by the bridge method.
They may also be used separately, as shown in the Drawing, or in various
combinations,
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Muirhead in the Great Seal Patent Office on the 21st December
1876.
JOHN MUIRHEAD, junior, of Stanley Villa, Thornton Hill, Wimbledon, in the
County of Surrey. "IMPROVEMENTS IN ELECTRIC TELEGRAPHS."
This Invention consists in improvements in the methods of working duplex
telegraphy, especially on submarine cables, in conjunction with compensating
circuits, whereby any want of perfect electric similarity between the cable and
artificial line can be compensated for or corrected, and also a gain of speed in
signalling obtained.
In ordinary working of submarine telegraph lines of any considerable length it
is usual to employ condensers either in the sending or receiving circuits, or in
both. In duplex working I use condensers sometimes placed between the battery
key and the junction of the branches of a Wheatstone bridge, as shown in
Figure 1.
Sometimes I use two condensers or sets of condensers, as in Figure 2, one set
being placed between the end of one branch of the bridge and the cable, and tho
other set between the other branch of the bridge and the artificial line or com-
pensating circuit. By this latter arrangement (which I shall call that of " bridge
condensers") it is found that the arms of the bridge may be greatly reduced in
resistance, and a consequent reduction in the retardation of the signals effected:
In this method of working the terminals of the receiving instrument may be con-
nected on the line side of the condensers with the cable and artificial line respect-
ively, as shewn at a, b, Figure 2; or the receiving instrument may be connected
with the opposite poles of the condensers on the bridge side, as shown by the
dotted lines m, n, in the same Figure. I prefer the latter arrangement.
I also employ condensers in circuit with the receiving instrument,
1st. Connected in the same manner as an ordinary shunt with the terminals of
the instrument, as at a, Figure 3.
2ndly. Or so connected that the condenser intervenes between one pole or
terminal of the receiving instrument and the junction of the cable or of the artificial
line with the arm of the bridge or with the bridge condensers, as at b, Figure 3.
I sometimes use both arrangements in combination.
In some cases where there is a difficulty in obtaining a perfect balance I employ
an arrangement of conductors which I call a "double bridge." To the ends of the
branches of the ordinary bridge remote from their junction with one another I
attach a conductor of adjustable resistance, an intermediate point of which I connect
either to earth, Figure 4, or to the junction of the bridge branches with one another;
either directly or through a resistance coil r, as in Figure 5, and with or without
condensers as circumstances may require.
Or sometimes I find it advantageous to move down to a point in the artificial
line, to be determined experimentally, that end of the said conductor which is
generally attached to the junction of the artificial line and one pole of the receiving
instrument. This arrangement is represented in Figure 5ª, and in another form in
Figure 5b.
I find it sometimes convenient as a means of perfecting the balance to make use
of an electro-magnetic adjustment either alone or in conjunction with some of the
adjustments above described. I insert the primary of an electro-magnetic coil with
moveable soft iron core between the sending key and the junction of the branches

page_text: of the bridge, the secondary (the resistance of which is adjustable) being connected
in one of the following manners:-
1st. Its ends are connected with the poles of the receiving instrument in the
manner of a shunt, as shown in Figure 6.
2nd. Or its ends are connected with those of the branches of the bridge, as shown
in Figure 7.
3rd. Or one of its ends is connected with one pole of the receiving instrument
and the other end with the junction of the cable or artificial line with its arm of
the bridge or bridge condensers, as shown in Figure 8.
.
4th. Or the secondary wire in parallel circuit with a suitable resistance coil is
used as one branch of the bridge itself, as in Figure 9.
I also sometimes insert the primary wire between the cable and one branch of
the bridge, whilst the secondary is inserted between the artificial line and the other
branch of the bridge, or vice versa, the requisite adjustment being effected by
placing resistance coils in parallel circuit with either wire as a shunt. This arrange-
inent is shown at Figure 10.
Another method of adjustment by which a balance is sometimes facilitated
consists in the addition of resistance coils between the earth terminals of any or all
the consecutive sections of the artificial line, or between the last earth terminal and
the earth itself. This has the effect of slightly increasing the retardation of the
artificial line. On the other hand should it be desirable to diminish the retardation,
I effect this by placing a coil of suitable high resistance between the line terminals
so as to be in parallel circuit with that part of the line whose retardation is too
great.
Instead of using ordinary resistance coils to form the branches of the bridge I
sometimes use two appropriate sections of artificial line.
As a means of removing disturbances that sometimes occur in the balance I have
found the arrangement shewn at Figure 11 effective. It consists of inserting small
resistances between the sets of "bridge condensers" and the cable and the
artificial line respectively. Either or both these resistances should be adjustable.
In my Patent No. 3374, September 27th, 1875, the same adjustment is shown in
Figure 2 as applied to the system of working in which the receiving condenser is
inserted either between the receiving instrument and cable or between the receiving
instrument and artificial line.
I also sometimes place these small resistances between the junctions of the bridge
with the receiving instrument and the "bridge condensers" above referred to. This
arrangement is shewn at Figure 12.
As an additional means of eliminating the disturbances of the balance I some-
times employ a condenser of small capacity, one of whose poles is connected to
earth, the other pole being connected to one branch of the bridge at a point best
ascertained by trial. This is shown at y in Figure 12.
I sometimes also use an arrangement of the bridge as shown at Figure 13, in
which one of the branches is composed of two or more conductors 7, 71, &c, one of
which is connected in the ordinary way to the beginning of the artificial line, the
other or others 1, 2, &c., of considerable resistance being connected to some point
or points x, x, &c., along the artificial line best determined by experiment. Or I
employ such a series of conductors 71, 72, 73, inserted between one pole of the
receiving instrument and different points x1, x2, x³, of the artificial line. This
arrangement is shown at Figure 13ª.
Sometimes in my method of working with bridge condensers I also employ
an arrangement of a condenser and a high resistance coil, as shown at Figure 14.
One pole of the condenser is connected through a high resistance to the end of one
of the branches of the bridge, the other pole being connected to earth.
All the above arrangements with the slight modification which will be evident to
electricians are equally applicable to the working with a differential receiving
instrument instead of by the bridge method.

page_text: They may also be used separately, as shown in the Drawing, or in various
combinations.
I claim my several improvements in connection with electric telegraphs sub-
stantially as described.
In witness whereof, I, the said John Muirhead, have hereunto set my hand
and seal, this Nineteenth day of December, in the year of our Lord One
thousand eight hundred and seventy-six.
J. MUIRHEAD, JR. (L.S.)