IMPROVEMENTS IN DUPLEX AND OTHER SYSTEMS OF ELECTRIC TELEGRAPHY
Year: 1885

page_text: I ALEXANDER MUIRHEAD of No 3 Elm Court, Temple, E.C. in the City of
London Telegraph Engineer do hereby declare the nature of my Invention for
IMPROVEMENTS IN DUPLEX AND OTHER SYSTEMS OF ELECTRIC TELEGRAPHY, to
be as follows:-
This invention relates to Duplex Telegraphs and the object of the same is to
effect greater and better results from the duplex working of long submarine cables
on systems such as that known now as the Muirhead double-block' system
described in Letters Patent No 2538 of 1877 granted to John Muirhead and myself,
or on any other analogous systems of working.
In the accompanying drawing Fig. 1 is a diagram showing the improved arrange-
ment of apparatus for carrying out part of the invention described in the above
Letters Patent and is substantially a reproduction of Fig. 4 of the drawings
accompanying the same; Fig. 2 is the similar arrangement adopted by us when
the receiving instrument employed is not wound differentially; Fig. 3 is a diagram
showing the arrangement and modification of the apparatus for carrying out the
present invention.
In Fig. 1 or Fig. 2 of the drawing C, and C, are the two sets of condensers
placed respectively between the key K and the cable C, and the key and the
artificial cable A. L. b, and b, are the two resistances forming what is called the
bridge. A and B in Fig. 1 are the two differential coils of the differentially
wound receiving instrument. In Fig. 2 the differential instrument is replaced by
the ordinary instrument R, in which there is only one circuit and C. the receiving
condenser.
It has been found practicable to establish and maintain a balance on short cables
(up to 500 miles) without using the bridge wires b₁ and b, by merely adjusting the
capacity of the condensers C, and C, relatively to each other. But I have since
discovered that on very long cables such as those recently laid between Canso in
Nova Scotia and Waterville in Ireland (the Mackay-Bennett Cables) that it is
insufficient and extremely difficult to effect and maintain in practice a sufficiently
close balance by merely having the con lensers C, and C, (sending condensers)
adjusted for capacity. In order to effect a balance sufficiently exact for the pur-
pose of obtaining the greatest possible speed of working it is necessary not only

page_text: that the capacity of the condenser C₁ placed between the key K and submarine
cable C. should be of the required ratio to that of the condenser C, between the
key and the artificial cable AL. but also that their times of charging and
discharging should be the same.
As it is practically impossible to construct or build up a number of sets of large
condensers even out of exactly the same materials, so that their rates of absorption
of charge shall be the same throughout I resort to the following device which is
the subject of this invention and which is illustrated in Fig. 3.
A rheostat Rh. of low resistances (+ ohms) is interposed between the signalling
key K, and the condensers C, and C. The cable C and the artificial cable A L.
are connected with these condensers in the manner shewn and a condenser C, and
receiving instrument R are inserted in the circuit between the real and artificial
cables. B. represents the battery and E. the earth. To one of the two condensers,
say C. I attach another and supplementary condenser C, which is subdivided into
small parts and I insert between one terminal of it and one terminal of C₂ a set of
coils, marked HR in the diagram, of high resistance (say of from 1,000 to
200,000 ohms) and I connect the other terminal of C₁ by a simple wire with the
corresponding terminal of C, as shown. In effecting the balance the artificial
cable A. L. is first of all made electrically equal to the cable C. The condensers C₁
and C, are then inserted and their capacities adjusted by means of a subdivided
condenser C. After obtaining in this way the nearest balance a slight increase is
made in the capacity of C,, say by 1 microfarad, and by trials the amount of
resistance required in the resistance coils HR is ascertained. This produces
a flow of charge in the circuit of C₂ and C, together equal to that flowing into the
condenser C₁.
By way of illustrating and explaining this improved method of balancing
I give the conditions required in balancing one of the above-mentioned Mackay-
Bennett cables which are as follows:-On the northerly of the two main cables C₁
is equal to 120 microfarads, C₂ to 120 microfarads, C, to 15 microfarad and the
resistance in HR 107,000 ohms.
In this case the combination of the small capacity in C, with the resistance of
the coils H R. produces a flow of charge of slower rate which superposed upon that
of the condenser C, produces the same effect upon the differential arrangement as
the charging and discharging of the condenser C₁.
The present invention is not limited to the herein before described system, but is
applicable to any other system of working telegraph cables in which it is required
to balance one cable against another by means of condensers either in the case of
double-cored (or multiple-cored) cables or cables under separate iron-sheathings.
It may sometimes facilitate the balancing of cables to have an adjustable set of
coils of high resistance similar to HR also placed in circuit with a portion of the
condenser C₁.
And in some cases it may be beneficial to increase the electro-magnetic capacity
of the coils of H R by winding a portion of them on iron cores.

page_text: COMPLETE SPECIFICATION.
Improvements in Duplex and other Systems of Electric
Telegraphy.
I ALEXANDER MUIRHEAD of N° 3 Elm Court, Temple E.C. in the City of
London, Doctor of Science, Electrical Engineer do hereby declare the nature of my
Invention for "IMPROVEMENTS IN DUPLEX AND OTHER SYSTEMS OF ELECTRIC
TELEGRAPHY" and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement :-
"
This invention relates to Duplex Telegraphs and the object of the same is to
effect greater and better results from the duplex working of long submarine cables
on systems such as that known now as the Muirhead "double-block system
described in the Specification of the Letters Patent No 2538 of 1877 granted to
John Muirhead and myself, or on any other analogous systems of working.
In the accompanying drawing Fig. 1 is a diagram showing the improved
arrangement of apparatus for carrying out part of the invention described in
of the
the above Specification and is substantially a reproduction of Fig.
drawings accompanying the same; Fig. 2 is the similar arrangement adopted by
us when the receiving instrument employed is not wound differentially; Figs. 3
and 4 are diagrams showing the arrangement and modification of the apparatus for
carrying out the present invention.
In Fig. 1 or Fig. 2 of the drawing C₁ and C, are the two sets of condensers
placed respectively between the key K and the cable C, and the key and the
artificial cable A. L. b, and b, are the two resistances forming what is called the
'bridge." A and B in Fig. 1 are the two differential coils of the differentially
wound receiving instrument.
In Fig. 2 the differential instrument is replaced by the ordinary instrument R,
in which there is only one circuit and C, the receiving condenser.
It has been found practicable to establish and maintain a balance on short cables
(up to 500 miles) without using the bridge wires b₁ and b₂ by merely adjusting the
capacity of the condensers C₁ and C₂ relatively to each other. But I have since
discovered that on very long cables such as those recently laid between Canso
in Nova Scotia and Waterville in Ireland (the Mackay-Bennett Cables) that it is
insufficient and extremely difficult to effect and maintain in practice a sufficiently
near balance by merely having the condensers C₁ and C₂ (sending condensers)
adjusted for capacity.
In order to effect a balance sufficiently exact for the purpose of obtaining the
greatest possible speed of working it is necessary not only that the capacity of the
condenser C₁ placed between the key K and the submarine cable C should be of
the required ratio to that of the condenser C₂ between the key and the artificial
cable A. L. but also that their times of charging and discharging should be
the same

page_text: .
As it is practically impossible to construct or build up a number of sets of large
condensers even out of exactly the same materials, so that their rates of absorption
of charge shall be the same throughout-I resort to the following device which is
the subject of this invention and which is illustrated in Fig. 3.
A. rheostat Rh of low resistances ( ohms) is interposed between the signalling
key K and the condensers C₁ and C. The cable C and the artificial cable A L are
connected with these condensers in the manner shewn and a condenser C₁ and
receiving instrument R, are inserted in the circuit between the real and artificial
cables. B. represents the battery and E the earth connection. To one of the two
condensers, say C₂ I attach another and supplementary condenser C, which is
subdivided into sinall parts and I insert between one terminal of it and one
terminal of C₂ a set of coils, marked H. R. in the diagram, of high resistance (say
of from 1,000 to 200,000 ohms) and I connect the other terminal of C3 by a simple
wire with the corresponding terminal of C₂ as shown. In effecting the balance the
artificial cable A. L. is first of all made electrically equal to the cable C. The
condensers C₁ and C, are then inserted and their capacities adjusted by means of
a subdivided condenser C. After obtaining in this way the nearest balance a
alight alteration is then made in the capacity of C3, say about 1 microfarad, and
by trials the amount of resistance required in the resistance coils H. R. is
ascertained. This produces a flow of charge in the circuit of C, and C, together
equal to that flowing into the condenser C₁.
By way of illustrating and explaining this improved method of balancing I give
the conditions required in balancing one of the above mentioned Mackay-Bennett
cables which are as follows;-On the northerly of the two main cables C, is equal
to 120 microfarads, C₂ to 120 microfarads, C, to 15 microfarad and the resistance
in H. R, 107,000 ohms. In this case the combination of the small capacity in C
with the resistance of the coils H. R. produces a flow of charge of slower rate
which superposed upon that of the condenser C₂ produces the same effect upon the
differential arrangement as the charging and discharging of the condensers C₁.
The present invention is not limited to the hereinbetore described system, but is
applicable to any other system of working telegraph cables in which it is required
to balance one cable against another by means of condensers either in the case of
double-cored (or multiple-cored) cables or cables under separate iron sheathings.
It may sometimes facilitate the balancing of cables to have an adjustable set of
coils of high resistance similar to H. R. also placed in circuit with a portion of the
condenser C. And in some cases it may be beneficial to increase the electro-
magnetic capacity of the coils composing the resistance circuit H. R. by winding
the whole or a portion of them on iron cores.
In Fig. 4 of the drawings is shewn the arrangement of apparatus to produce
this effect. W is a bobbin provided with an iron core x, x for the purpose of
'increasing the electro-magnetic capacity of the circuit when required to do so.
The iron core fitting into the bobbin upon which the wire is wound is made
adjustable. The core is composed of two sections, one, x, of soft iron, which is the
magnetizable section and the other, a¹ of non-magnetic material such as brass.
The two sections are united by a bevelled joint as shewn in Fig. 4, which
construction permits of a gradual and careful adjustment of the amount of
magnetic material within the coil and bobbin, W.
The extremities of the core are so mounted that the core may be moved through
the bobbin in the direction of its length by means of an adjusting screw or other
convenient mechanism. Any convenient or desirable number of such inductors
may be used either with or without the resistance coils H. R.
In certain cases it has been found advisible to apply independent resistance
circuits to both of the condensers C, and C₁ of the differential arrangement and
this is now actually done upon the long submarine cables between Waterville,
Ireland, and Canso, Nova Scotia. In such cases the electro-magnetic inductor, W,
may be introduced into either one or both of the resistance circuits in connection

page_text: with the supplementary condenser, C, and either with or without the resistance
coils H. R. as before.
Having now particularly described and ascertained the nature of my said
Invention and in what manner the same is to be performed I declare that what
I claim is
In connection with an electrical or telegraphic circuit the combination of a
subdivided or adjustable condenser with either an adjustable set of ordinary
resistance coils or of coils wound either wholly or partly on bobbins having
adjustable iron cores substantially as and for the purpose hereinbefore described.
Dated this 5th day of October 1885