Year: 1888

page_text: Date of Application, 11th Feb., 1888
Complete Specification Left, 12th Nov., 1888
Complete Specification Accepted, 11th Feb., 1889
I, ALEXANDER MUIRHEAD, Doctor of Science, Telegraph Engineer, of Cowley
Street, Westminster, in the County of Middlesex, do hereby declare the nature of
this invention to be as follows:-
My invention relates to duplex electric telegraphs and its main object is to
diminish the cost of the apparatus required for working long submarine cables upon
systems such as that known as the Muirhead "double-block" system.
In the said "double-block" system and analogous systems it has been usual to
employ an artificial line or cable, and condensers arranged respectively between the
key and the actual line or cable and between the key and the artificial line or
cable.
Heretofore, it has been usual to make the artificial line of the same electrical
dimensions as the actual cable, that is to say, to use an artificial line the ratio of
whose resistance to capacity is the same as that of the resistance of the cable to the
capacity of the cable.
.
I have discovered that a sufficiently near balance can be obtained to permit efficient
duplex working, with an artificial line of much less capacity than the cable. For
this purpose I increase the resistance of the artificial line in such a manner that,
although the capacity thereof is less than that of the cable, the product of the
resistance and the capacity of the artificial line is equal to the product of the resist-
ance and capacity of the cable.
I sometimes substitute for the said artificial line or cable a series of condensers
which are of less total or collective capacity than the main condensers (that is to say,
those above referred to), and which are arranged in combination with suitable
resistances. In some instances, I employ a supplementary condenser in combina-
tion with one of the said main.condensers as hereinafter described.
When a differential receiving instrument can be employed, I sometimes dispense
with the condenser heretofore used between the key and the artificial line or cable
and connect one wire of the said receiving instrument directly to my series of
condensers.
In the accompanying drawing
Figure 1 is a diagram showing an arrangement of apparatus of the kind or class
described in the Specification of former Letters Patent granted to me and dated

page_text: Figure 2 is a diagram illustrating a modification of my invention.
Figure 3 is a diagram somewhat similar to Figure 1 showing another modification
of my invention.
Figures 4 and 5 are diagrams.illustrating other modifications thereof.
Referring to Figure 1, is the cable. U¹, C are the main condensers arranged
respectively between the key K and the said cable and between the said key and
the artificial cable A, L. Rh. is a rheostat of low resistance placed between the
key K and the condensers C1, C2. C³ is a supplementary condenser connected to
the condenser C, and H. R is a set of coils of high resistance inserted between
terminals of the said condensers 02, 0³. I sometimes substitute for the condenser C³
and resistance H. R, a circuit composed of what is now known as "Muirhead's
Inductive Resistance as shown in Figure 2, wherein a, y is the resistance strip
or conductor of the Inductive Resistance and C4 is the induction plate or surface.
A receiving instrument R and a condenser (are inserted in the circuit between
the real and artificial cables.
Referring to Figure 1, the following is a practical example of the conditions
under which I can advantageously use an artificial line of less capacity than the
cable, that is to say :-
Assuming the cable to have a capacity of 1000 microfarads and a resistance
of 7,500 Ohms, I make the artificial line with a capacity of 500 microfarads and a
resistance of 15,000 Ohms. To establish the balance in such a case, the condenser C¹
must have a capacity of 80 microfarads, the condenser C a. capacity of 38.23
microfarads and the condenser C³ a capacity of 3.3 microfarads, and HR should
be 31,000 Ohms. It is also necessary to insort a resistance of about 20 Ohms
between and the Rheostat Rh. When the artificial line is of very high resist-
ance it may be advantageous, in certain cases, to put the key K in place of the
receiving instrument R and vice versa, as shown in Figure 3.
Figure 4 shows an arrangement of apparatus similar to that shown in Figure 1
with the following exception, viz. --I dispense with the artificial cable and substitute
therefor a series of condensers c¹, c², c³, ct, c5 of relatively small capacity, which are
all connected to the main condenser C2 and to earth, resistances 1, 72, 73, 74,
being interposed between the several condensers of the said series and the earth.
The condenser 2 is, moreover, connected to earth through a resistance R¹.
2,5
Figure 5 shows an arrangement in which a differential receiving instrument is to be
employed. A, B indicate the two wires or coils of this instrument, whose relative
electro-magnetic effect upon the index of the instrument can be varied. The wire A
is inserted between the condenser C₁ and the rheostat Rh. 1. dispense with the
main condenser O2 and with the supplementary condenser 03 shown in the preceding
Figures and I connect one end of the wire B, to the rheostat Rh., and the other
end thereof to condensers c¹, c2 &c. and resistances 1, 2 &c. which are connected
to earth, and I also connect the said wire B to earth through a resistance R¹..
The condensers c¹, c² &c. and resistances 1, 2 &c. may, in any case, be arranged
either as shown in Figure 4, or as in Figure 5, that is to say, the resistances may
be between the condensers and the earth or between the condensers and the receiving
instrument.
Any desired number of condensers and resistances may be employed in the afore-
said series.
It is evident that, by the improvements illustrated in Figure 5, I provide for
greatly diminishing the cost of the apparatus, as I obviate the necessity for employing
a large condenser such as has heretofore been used in combination with the artificial
line or cable.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C.,
Agents for the Applicant.

page_text: Improvements relating to Electric Telegraphs.
I, ALEXANDER MUIRHEAD, Doctor of Science, Telegraph Engineer, of Cowley
Street, Westminster in the County of Middlesex do hereby declare the nature of
this invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:—
My invention relates to duplex electric telegraphs, and its main object is to
diminish the cost of the apparatus required for working long submarine cables upon
systems such as that known as the Muirhead "double-block" system.
In the said "double-block" system and in analogous systems, it has been customary
to employ an artificial line and to arrange condensers or sets of condensers between
the key and the actual line or cable and between the key and the artificial line. It
has, moreover, been usual to make an artificial line with a total capacity equal to or
nearly as great as that of the cable, and in which the ratio of the resistance to the
capacity is the same as that of the resistance of the cable to the capacity of
the cable
I have discovered that a sufficiently near balance to permit of efficient duplex
working can be obtained with an artificial line of much less total capacity than that
of the cable. To effect this result I, in some cases, increase the resistance of the
artificial line in such a manner that, although the capacity thereof is less than that of
the cable, the product of the resistance and the capacity of the artificial line is equal
to the product of the resistance and capacity of the cable. For example, I substitute
for the artificial line heretofore employed, an artificial line consisting of Muirhead's
"Inductive Resistance" (such as that described or referred to in the specifications
of the following former Letters Patent, viz. :-No. 3663 dated 23rd October 1874
and No. 2538 dated 2nd July 1877) so constructed that its strip resistance is
greater in proportion to its capacity than in apparatus of the same kind or class
heretofore constructed. In other cases, I substitute for the artificial line beretofore
employed, a compensating circuit composed of a series of condensers of which the
total or collective capacity is less than the total capacity of the cable (say for instance
about one third of the capacity of the cable), and which are arranged in com-
bination with suitable resistances, the said series of condensers and resistances being
connected to one of the main condensers.
Moreover I employ a supplementary condenser and a high resistance in
combination with one of the condensers or sets of condensers above mentioned
composing the double-block; or I employ other suitable means for establishing a
balance under the conditions of cable and artificial line herein specified
In some cases, the condenser employed in combination with the compensating
circuit above described may be dispensed with, a differential receiving instrument
being used, one wire of which is connected directly to the compensating circuit and
the other to the condenser which is in connection with the cable. In such cases,
the valves of the condensers and resistances forming the compensating circuit must
be determined so as to produce the same electrical effect as that obtained by means

page_text: of a compensating circuit such as that above described combined with a main
condenser.
In the accompanying drawing
Figure 1 is a diagram showing an arrangement of apparatus of the kind or class
referred to in the Specification of former Letters Patent granted to me and dated
5th January A.D. 1885, No. 154 and having my present improvements embodied
therein or incorporated therewith.
Figure 2 is a diagram illustrating a modification of my present invention.
Figures 3, 4 and 5 are diagrams illustrating further modifications thereof.
Like letters indicate corresponding parts throughout the drawing.
Referring to Figure 1, C is the cable. A L is the artificial line which consists, as
I above stated, of Muirhead's Inductive Resistance, a, y being the resistance-strip or
conductor and the induction plate or surface. C, 2 are the main condensers
arranged respectively between the key K and the said cable and between the said key
and the artificial cable A L. R is a rheostat of low resistance placed between the
key K and the condensers 01, 02. 03 is a supplementary condenser connected to the
condenser C2, and H R is a set of coils of high resistance inserted between terminals
of the said condensers C2, C3. I sometimes substitute for the condenser C³ and
resistance HR, a circuit composed of Muirhead's Inductive Resistance as shown in
Figure 2, wherein a,y is the resistance-strip or conductor of the said Inductive
Resistance and C+ is the induction plate or surface. A receiving instrument R and a
condenser Care inserted between the real and artificial cables.
:―
The following is a practical example of the conditions under which I can advan-
tageously use an artificial line of less capacity than the cable, that is to say, assuming
the. cable C, Figure 1, to have a capacity of 1000 microfarads and a resistance of
7,500 Ohms, a balance is established with the artificial line of total capacity of 500
microfarads and a resistance of 15,000 Ohms under the following conditions, viz. :-
the condenser having a capacity of 80 microfarads, the condenser C³ a capacity of
38-23 microfarads, and the condenser C³ a capacity of 3:3 microfarads, and HR
31,000 Ohms; a resistance of about 20 Ohms being inserted between C¹ and the
rheostat R h. When the artificial line is of very high resistance, it may be
advantageous, in certain cases, to transpose the key K and receiving instrument R, as
shewn in Figure 3.
Figure 4 shows an arrangement of apparatus similar to that shown in Figure 1
with the following exception, viz. :-I dispense with the artificial cable and substitute
therefor a compensating circuit comprising a series of condensers c¹, c², c³.c³, c³ of
relatively small capacity, which are all connected to the main condenser C2 and to
earth, resistances 70; 22, 23, 24, 28, being interposed between the several condensers of
the said series and the earth. The condenser C' is, moreover, in some cases, connected
to earth through a resistance R¹.
Figure 5 shows one arrangement in which a differential receiving instrument is
employed; A, B indicate the two wires or coils of the said receiving instrument,
whose relative electro-magnetic effect upon the index of the instrument can be varied.
The wire A is inserted between the condenser C¹ and the rheostat Rh. I dispense
with the main condenser C² and with the supplementary condenser (³ and resistance HR
shown in the preceding Figures, and I connect one end of the wire B to the
rheostat Rh, and the other end thereof to the condensers c¹, c², c³, c1, c³ and
resistances 1, 2, 3, 7, 8, the said condensers being connected to earth; and, in some
cases, I also connect the said wire B to earth through a resistance R¹. It is evident
that the values of these condensers and resistances must differ from the values of those
used in combination with the condenser C² as in Figure 4.
The condensers c¹, c², c³, c, co and resistances 71, 72, 73 may in any case be
arranged either as shown in Figure 4 or as in Figure 5, that is to say, the resistances
may be between the condensers and the earth or between the condensers and the
receiving instrument.
Any desired number of condensers and resistances may be employed in the afore-
said series. _

page_text: It is evident that, by the improvements above described, I provide for greatly
diminishing the cost of the apparatus, as I am enabled to employ apparatus of much
less capacity than has heretofore been used in duplex telegraphs on submarine cables.
Moreover a diminished capacity is required in a series of condensers and resistances
such as that above described, as compared with an artificial line of ordinary
construction.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed I declare that what I
claim is
“
or
First. In a duplex electric telegraph working upon the double-block'
analogous systems and in which condensers are employed in both the sending and
receiving circuits an artificial line consisting of Muirhead's Inductive Resistance
having a total capacity much less than that of the actual cable and resistance
correspondingly greater than that of the conductor of the cablo, substantially as, and
for the purpose, above specified.
Second. In a duplex electric telegraph working on the double-block or analogous
systems and in which condensers are employed in both the sending and receiving
circuits, the combination of an artificial line or compensating circuit whose capacity
is much less than that of the actual cable and whose resistance is correspondingly
greater than that of the said cable, and means substantially as described for establishing
a balance under the conditions of cable and artificial line above specified.
Third. In a duplex electric telegraph constructed on the double-block or analogous
systems, a compensating circuit comprising a series of condensers and resistances,
substantially as above described.
Fourth. The modification of my invention substantially as described with reference
to Figuro 5 of the drawing, for the purpose specified.
Dated this 19th ave of November 1888
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London,
Agents for the Applicant.