IMPROVEMENTS IN ELECTRIC TELEGRAPHS
Year: 1877

page_text: LETTERS PATENT to John Muirhead, junt. and Alexander Muirhead, both
of No. 29, Regency Street, in the City of Westminster, for the Invention of
"IMPROVEMENTS IN ELECTRIC TELEGRAPHS."
Sealed the 15th September 1877, and dated the 2nd July 1877.
PROVISIONAL SPECIFICATION left by the said John Muirhead and Alexander
Muirhead at the Office of the Commissioners of Patents on the 2nd July
1877.
JOHN MUIRHEAD, junt, and ALEXANDER MUIRHEAD, both of No. 29, Regency
Street, in the City of Westminster. "IMPROVEMENTS IN ELECTRIC TELEGRAPHS."
In the following Invention we sometimes make use of an apparatus described in
the Specification of a Patent, No. 3663, dated October 23rd, 1874, taken out by one
of us, and to which Patent a Disclaimer has been filed. Such apparatus consists, to
describe it briefly, of two plates or surfaces of metal or other conducting material
separated by a di-electric.
The area of the opposed surfaces, the thickness and nature of the di-electric
between them, determine the capacity or power of condensation of the instrument.
One plate has but a single connection, like the plate of an ordinary condenser. The
other plate has two connections, and is divided into a continuous strip, or is other-
wise arranged to give any resistance which may be required between these con-
nections or terminals. Such an instrument (with the case which contains it) may
conveniently and to avoid repetition be called an inductive resistance box.'
The first improvement consists in making use of such inductive resistance to form
the differential sending circuits for duplex working in lieu of the combination of
ordinary condensers with a bridge of resistance coils generally in use.
We employ sufficient inductive resistance boxes to give the capacity found neces-
sary for the efficient duplex working of the line, and we make use of the strip or
conducting part of the boxes to effect the balance of charge between the cable and
compensating circuit. This arrangement is illustrated by Figures 1 and 2, in
which A, b, 62, consists of Muirhead's inductive resistance boxes; A, the capacity
plate; and b and 6%, resistance strips; R, the receiving instrument (recorder or
mirror); C, the receiving condenser.

page_text: The similar case with the usual bridge of resistance coils is shown at Figure 3.
A, the sending condenser; C, the receiving condenser ; and b1, b2, the bridge.
When the receiving instrument used is wound with two separate coils, the
ordinary arrangement would be as is illustrated by Figure 4, in which C¹, C², are
the bridge condensers; A, B, two circuits in a differential instrument.
Figure 5 illustrates a corresponding arrangement, making use of inductive
resistances in accordance with our Invention. Adjustment is effected by varying
one of the resistances b1, b2, and capacity of one of the portions a', a², of the inductive
resistances; is an adjustable resistance.
Another part of this Invention has reference to improvements whereby saving in
apparatus is effected. On long cables, such as the Suez-Aden or Aden-Bombay
sections of the Eastern Telegraph Company's system, the effect of a want of total
capacity in the compensating circuit may be counteracted by connecting the
receiving circuit with some distant point in the compensating circuit in such a
manner that the potential of the two ends of the receiving instrument shall be
equal during the whole duration of the contact with the battery, so as not to disturb
its action in recording the received signals.
Figures 6, 7, 8, 9, 10, 11, and 12 are various methods we have adopted to effect
this.
In these Figures C¹ represents the sending condenser placed generally between
the signalling key and the bridge or other differential apparatus; C³, the receiving
condenser, 3, and 4, high resistances. The receiving condenser C2 is
generally connected up between the junction of cable and the differential or bridge
arrangement and one terminal of the recording instrument.
In the above Figures a few plates c² of the receiving condenser Care disconnected
from the instrument and connected through a high resistance to a point x on the
conductor of the compensating circuit; this point to be found by experiment. The
resistance ¹ connecting the plates c2 with the point is adjustable.
The adjustment is much facilitated (see Figure 7) by connecting up a series of
resistance coils 4 (in slide form) between C2 and Y, and varying the position of y
on by means of a sliding contact.
In conjunction with the form of adjustment shewn on Figure 6, we sometimes use
an, adjustable condenser C3, shown on Figures 8, 10, 11, and 12, connected between
the fork of the differential F and some point y on the coil ***.
In Figures 9, 10, 11, and 12 is shown the arrangement when the recording
instrument has two separate coils (A and B); in all these cases, having condensers
both in the sending and receiving circuit, when the total capacity of the compen
sating circuit is considerably less than that of the cable, it is found necessary to put
the distant end of the artificial line (or conductor of the compensating circuit), to
earth through a resistance. The less the capacity of the artificial line the greater
this resistance will have to be.
On short cables, where condensers in the sending and receiving circuits are dis-
pensed with, Figure 11 shows the arrangement.
In some cases, especially when the speed of working adopted does not approachi
the limit the particular cable is capable of, a still further reduction of the total
capacity of the artificial line may be made, and may be compensated for by means
of the circuit. Y, B, ¹, C, E, (see Figures 10 and 11), in conjunction with the adjust-
ments a and b, Y,,C³, 75, E, and F, C³, y. .Here the compensating part of the duplex
arrangement is divided into two or more separate circuits (composed either of the
inductive resistances above described, or of ordinary resistance coils and condensers)
in parallel order, some operating through separate parts of the receiving circuit, or
through separate parts of the receiving instrument itself. For example, in Figures 10
and 12, the two circuits X, C2, c², B, ³, (C) E and Y, b, 3, E, together form the
compound compensating circuit, the first having direct effect on a part of the
receiving instrument (B) itself. The resistances 1 and 2 and capacity c² can be
arranged to dispense with a large quantity of apparatus in the ordinary artificial
line.

page_text: In arrangements similar to Figure 11 we prefer to use for the branches Y, b, 72; E,
and r¹, C, E, inductive resistance boxes, having greater ratio of resistance to capacity
than the cable; or in place of Y, b, 2, E, a series of circuits of resistances and con-
densers in multiple arc may be used, and the final adjustment effected by means of
the circuit 1, C4, E.
In the first part of this Specification we describe the use in the differential part
of the duplex arrangement of Muirhead's inductive resistance boxes as ordinarily
made for artificial lines.
Figures 13, 14, 15, and 16 illustrate. other methods of using such resistances:
having slightly different construction. We employ in these arrangements inductive;
resistances constructed of two parallel strips of tinfoil separated by .a di-electric, and
so arranged as to form two separate conducting circuits. In Figures 13, 14, 15,
and 16, S, T, and R, P, are the terminals of the two strips.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed by
the said John Muirhead and Alexander Muirhead in the Great Seal Patent
Office on the 2nd January 1878.
JOHN MUIRHEAD, junt, and ALEXANDER MUIRHEAD, both of No. 29, Regency
Street, in the City of Westminster. "IMPROVEMENTS IN ELECTRIC TELEGRAPHS."
In the following Invention we sometimes make use of an apparatus described in
the Specification of a Patent No. 3663, dated October 23rd, 1874, taken out by one
of us, and to which Patent a Disclaimer has been filed. Such apparatus consists, to
describe it briefly, of two plates or surfaces of metal or other conducting material
separated by.a di-electric.
The area of the opposed surfaces, the thickness and the nature of the di-electric.
between them, determine the capacity or power of condensation of the instrument.
One plate has but a single connection, like the plate of an ordinary condenser; the
other plate has two connections, and is divided into a continuous strip, or is other-
wise arranged to give any resistance which may be required between these con-
nections or terminals. Such an instrument (with the case which contains it), may
conveniently and to avoid repetition be called an inductive resistance box.
The first improvement in this Invention consists in making use of such inductive
resistance to form the differential sending circuits for duplex working in lieu of the
combination of ordinary condensers with a bridge of resistance coils generally.
in use.
We employ sufficient inductive resistance boxes to give the capacity found
necessary for the efficient duplex working of the line, and we make use of the strip.
or conducting part of the boxes to effect the balance of charge between the cable
and compensating circuit. This arrangement is illustrated by Figures: 1 and 2, in
which A, b, b, consists of Muirhead's inductive resistance boxes; A, the capacity.
plates; and band b², resistance strips; R, the receiving instrument (recorder or.
mirror); C, the receiving condenser.
The similar case with the usual bridge of resistance coils is shown at Figure 3.,
A, the sending condenser; C, the receiving condenser; and b¹, b², the bridge.
When the receiving instrument used is wound with two separate coils tho
ordinary arrangement would be as is illustrated by Figure 4, in which C¹, C², are
the bridge condensers; A, B, two circuits in a differential instrument.
'

page_text: Figure 5 illustrates a corresponding arrangement, making use of inductive
resistances in accordance with our Invention. Adjustment is effected by varying
one of the resistances 61, 62, and the capacity of one of the portions a¹; a², of the
inductive resistances; is an adjustable resistance.
Figure 5 shows another arrangement in which in accordance with this Invention
inductive resistances are employed in the bridge. The arrangement is adapted to
counteract the effect of any slight variation in the lines, or in the apparatus after
having once established the balance. We place two portions of inductive resist-
ance R¹ R², between the terminals of the bridge (X, Y) and the cable and the
artificial line connecting the outer or capacity plates (S1, S2,) together through a
separate circuit (g) in the receiving instrument. For this purpose portions (R¹,
and R) of inductive resistance exactly equal to each other both in capacity and
resistance should be taken, and they should be made as uniformly as possible.
Another part of this Invention has reference to improvements whereby saving in
apparatus is effected. On long cables, such as the Suez-Aden or Aden-Bombay sections
of the Eastern Telegraph Company's system, the effect of a want of total capacity in
the compensating circuit may be counteracted by connecting the receiving circuit
with some distant point in the compensating circuit in such a manner that the
potential of the two ends of the receiving instrument shall be equal during the
whole duration of the contact with the battery, so as not to disturb its action in
recording the received signals.
Figures 6, 7, 8, 9, 10, 11, and 12 are various methods we have adopted to effect
this.
In these Figures C³ represents the sending condenser, placed generally between
the signalling key and the bridge, or other differential apparatus; C2, the receiving
condenser; 1, 2, 3, and 4, high resistances. The receiving condenser C2 is
generally connected up between the junction of the cable and the differential or
bridge arrangement, and one terminal of the recording instrument.
In the above Figures a few plates c² of the receiving condenser C2 are disconnected
from the instrument and connected through a high resistance 71 to a point x on the
conductor of the compensating circuit, this point to be found by experiment; the
resistance connecting the plates c² with the point is adjustable.
The adjustment is much facilitated (see Figure 7) by connecting up a series of
resistance coils 7 (in slide form) between C2 and Y, and varying the position of y
on by means of a sliding contact.
In conjunction with the form of adjustment shewn on Figure 6, we sometimes
use an adjustable condenser C³, shown on Figures 8, 10, 11, and 12, connected
between the fork of the differential F and some point y on the coil
In Figures 9, 10, 11, and 12 is shewn the arrangement when the recording
instrument has two separate coils (A and B). In all these cases having condensers
both in the sending and receiving circuits, when the total capacity of the compen-
sating circuit is considerably less than that of the cable, it is found necessary to put
the distant end of the artificial line (or conductor of the compensating circuit) to
earth through a resistance ². The less the capacity of the artificial line the greater
this resistance will have to be.
On short cables, where condensers in the sending and receiving circuits are
dispensed with, Figure 11 shews the arrangement,
In some cases, especially when the speed of working adopted does not approach
the limit the particular cable is capable of, a still further reduction of the total
capacity of the artificial line may be made, and may be compensated for by means
of the circuit Y, B, r, C, E, (see Figures 10 and 11) in conjunction with the adjust-
ment a and b, Y, C5, 5, E, and F, C, y. Here the compensating part of the duplex
arrangement is divided into two or more separate circuits (composed either of the
inductive resistances above described, or of ordinary resistance coils and condensers)
in parallel order, some operating through separate parts of the receiving circuit, or
through separate parts of the receiving instrument itself. For example, in Figures 10
and 12 the two circuits X, C2, c², B, r¹, (C³), E, and Y, 6, 72, E, together form the

page_text: compound compensating circuit, the first having direct effect on a part of the
receiving instrument (B) itself. The resistances 71 and 72 and capacity c² can be
arranged to dispense with a large quantity of apparatus in the ordinary artificial
line.
In arrangements similar to Figure 11 we prefer to use for the branches Y, b, r², E,
and, C, E, inductive resistance boxes, having greater ratio of resistance to
capacity than the cable; or in place of Y, b, 2, E, a series of circuits of resistances
and condensers in multiple arc may be used, and the final adjustment effected by
means of the circuit r, C, E.
In the first part of this Specification we describe the use in the differential part
of the duplex arrangement of Muirhead's inductive resistance boxes as ordinarily
made for artificial lines.
Figures 13, 14, 15, and 16 illustrate other methods of using such inductive
resistances having slightly different construction. We employ in these arrangements
inductive resistances constructed of two parallel strips of tinfoil separated by a
di-electric, and so arranged as to form two separate conducting circuits. In Figures
13, 14, 15, and 16, S, T, and R, P, are the terminals of the two strips.
Having thus described the nature of our said Invention and the manner of
performing the same, we would have it understood that we claim,―
"
First. The application of "induction resistances" to form the 'bridge" or
differential sending circuits for duplex working.
Second. The several methods of constructing the "bridge" shown by and
described in respect to Figures 1, 2, 5, 5*, 13, 14, 15, and 16.
Third. The means of counteracting the want of capacity in the compensating
circuit by establishing a connection between the receiving circuit and a distant point
in the compensating circuit or artificial line.
Fourth. The several methods of establishing a connection between the receiving
circuit and a distant point in the compensation circuit shown by and described in
respect to Figures 6, 7, 8, 9, 10, 11, and 12.
Fifth. In combination with the connection between the receiving circuit and the
distant point of the compensating circuit, the further adjustment F, CS, 3, 7, shown
by and described in respect to Figures 8, 10, 11, and 12.
Sixth. In combination with the connection between the receiving circuit and the
distant point of the compensating circuit, the further adjustments Y, C5, 25, E,
and a and b, shown by and described in respect to Figures 10, 11, and 12.
In witness whereof, we, the said John Muirhead, jun., and Alexander
Muirhead, have hereunto set our hands and seals, this First day of
January, in the year of our Lord One thousand eight hundred and seventy-
eight.
J. MUIRHEAD, JR. (L.S.)
ALEX. MUIRHEAD. (L.S.)