IMPROVEMENTS IN ELECTRIC TELEGRAPHS
Year: 1875

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."
Sealed the 3rd March 1876, and dated the 27th September 1875.
PROVISIONAL SPECIFICATION left by the said John Muirhead at
the Office of the Commissioners of Patents, with his Petition, on
the 27th September 1875.
I, JOHN MUIRHEAD, junior, of Stanley Villa, Thornton Hill,
Wimbledon, in the County of Surrey, do hereby declare the nature of
the said Invention for "IMPROVEMENTS IN ELECTRIC TELEGRAPHS," to be
as follows:-
This Invention has for its object improvements in electric telegraphs.
For the purpose of duplex telegraphy where signalling is carried on
simultaneously from both ends of the line, an "artificial line" is
employed having resistance and capacity equal or suitably related to the
resistance and capacity of the cable or real line.

page_text: In constructing the artificial line according to this Invention I
employ a metallic wire of material and dimensions to give me the
resistance I require; this wire is the conductor of my artificial line. To
obtain the necessary capacity I cover the wire with an insulator (by
preference I wind a strip of paraffined paper around it), and over the
paraffined paper I wind a very thin conducting strip (copper by
preference) in a close spiral. The wire thus covered is wound for use
on a cylindrical frame of large diameter, and an earth connection is
made with the outer metallic covering.
I sometimes flatten the inner wire or conductor of the artificial line, 1
or use a hollow wire or wire of a section other than circular, as a
convenient means of adjusting the capacity to the resistance.
Another way of constructing the artificial line is with sheets of
tinfoil, in pairs, separated by an imperfect dielectric. I employ paper
saturated with glycerine or paper containing a small percentago of
plumbago, and this paper forms the conductor of the artificial line. The
resistanco can be adjusted to the capacity, in this case, by varying the
amount and nature of the material with which the paper is prepared and
the substance of the paper.
It is not necessary in constructing the artificial lines for duplex i
telegraphy on submarine lines that the ratio of the conductive resistance
to the electrostatic capacity should be the same as the ratio of the
resistance per knot to the capacity per knot of the cable to be balanced.
A good balance can be effected so long as the product of these quantities
is the same in the artificial line and in the cable, the times of charging å
conductors of great capacity to a given potential being proportional to
the product of resistance and capacity. And as it is necessary to have
great area of conducting material in order to get the same total capacity
as that of long cables, it is more economical to construct the artificial
lines with greater resistance and correspondingly less capacity.
The second part of my Invention consists of methods of eliminating
the disturbances or "kicks" that take place on the receiving instru-
ments used in "duplex" working on telegraph lines, submarine or
otherwise, arising from the induction of the charges sent into the real
and the artificial circuits. Thero are two ways by which I effect
this,―
1st Ru combining the annaratus in such
manner that immediately

page_text: In cases where the main line is faulty I introduce leakago circuits
through regulated resistances into the artificial line, the arrangement
is indicated in Figure 4, at x, a point depending on the position of the
fault or the resultant fault of the main line.
The above methods are for the most part also applicable to other
systems of "duplex" working, as for example those in which the
receiving instruments are used differentially. Two or more of them may
also be used in combination.
When, as in the method generally adopted for working long cables,
the conductor of the cable is insulated at both ends with condensers,
the conductor of the artificial line for duplex working is also insulated
in a similar manner; but I find it more economical to leave the distant
end of the conductor of the artificial line free, and to place a smaller
condenser (say of about one-third of the capacity of the condensers at
the near end) at a point intermediate of the length of the artificial line.
The proper point is easily ascertained by trial; the arrangement is
shewn at Figure 5. This constitutes another part of my Invention.
According to the last part of my Invention, instead of placing a
condenser between the receiving instrument and the earth, in ordinary
working I prefer to insert a coil of high resistance and great capacity.
Such a resistance may be made of the wire described above. In this
method permanent connection is made between the instrument and the
earth through this high resistance.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said John Muirhead in the Great Seal Patent Office 2
on the 27th March 1876.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOHN
MUIRHEAD, junior, of Stanley Villa, Thornton Hill, Wimbledon, in the
County of Surrey, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her 8
Letters Patent, bearing date the Twenty-seventh day of September, in
the year of our Lord One thousand eight hundred and seventy-five,
in the thirty-ninth year of Her reign, did, for Herself, Her heirs and

page_text: successors, give and grant unto me, the said John Muirhead, jr., Her
special license that I, the said John Muirhead, jr., my executors,
administrators, and assigns, or such others as I, the said John
Muirhead, jr., my executors, administrators, and assigns, should at any
time agree with, and no others, from time to time and at all times
thereafter during the term therein expressed, should and lawfully
might make, use, exercise, and vend, within the United Kingdom of
Great Britain and Ireland, the Channel Islands, and Isle of Man, an
Invention for "IMPROVEMENTS IN ELECTRIC TELEGRAPHS," upon the
condition (amongst others) that I, the said John Muirhead, jr.,
my executors or administrators, by an instrument in writing under
my, or their, or one of their hands and scals, should particularly
describe and ascertain the nature of the said Invention, and in what
manner the same was to be performed, and cause the same to be
filed in the Great Seal Patent Office within six calendar months next
and immediately after the date of the said Letters Patent.
NOW KNOW YE, that I, the said John Muirhead, jr., do hereby
declare the nature of the said Invention, and in what manner the
same is to be performed, to be particularly described and ascertained
in and by the following statement thereof, that is to say :—
This Invention has for its object improvements in electric telegraphs.
For the purpose of duplex telegraphy, where signalling is carried on
simultaneously from both ends of the line, an "artificial" line is
employed, having resistance and capacity equal or suitably related to
the resistance and capacity of the cable or real line.
In constructing the artificial line according to this Invention I
employ a metallic wire of material and dimensions to give me the
resistance I require; this wire is the conductor of my artificial line.
To obtain the necessary capacity I cover the wire with an insulator (by
preference I wind a strip of paraffined paper around it), and over the
paraffined paper I wind a very thin conducting strip (copper by pre-
ference) in a close spiral; the wire thus covered is wound for use on a
cylindrical frame of large diameter, and an earth connection is made
with the outer metallic covering.
I sometimes flatten the inner wire or conductor of the artificial line,
or use a hollow wire or wire of a section other than circular, as a
convenient means of adjusting the capacity to the resistance.

page_text: Another way of constructing the artificial line is with sheets of tin-
foil in pairs separated by an imperfect dielectric. I employ paper
saturated with glycerine or paper containing a small per-centage of
plumbago, and this paper forms the conductor of the artificial line. The
resistance can be adjusted to the capacity in this case by varying the
amount and nature of the material with which the paper is prepared and
the substance of the paper.
It is not necessary in constructing the artificial lines for duplex
telegraphy on submarine lines that the ratio of the conductive resistance
to the electrostatic capacity should be the same as the ratio of the
resistance per knot to the capacity per knot of the cable to be balanced.
A good balance can be effected so long as the product of these quantities
is the same in the artificial line and in the cable, the times of charging
conductors of great capacity to a given potential being proportional to
the product of resistance and capacity; and as it is necessary to have
great arca of conducting material in order to get the same total capacity
as that of long cables it is more economical to construct the artificial
lines with greater resistance and correspondingly less capacity.
The second part of my Invention consists of methods of climinating
the disturbances or "kicks" that take place on the receiving instru-
ments used in "duplex" working on telegraph lines, submarine or
otherwise, when the artificial line is imperfectly constructed, arising
from the induction of the charges sent into the real and the artificial
circuits; there are two ways by which I effect this,—'
First. By combining the apparatus in such a manner that immediately
in connection with the receiving instrument there shall be no circuit
of high capacity. In the case of the bridge method of ". 'duplex"
working I do this by either placing the receiving instrument between
two intermediate points in the two sides of the bridge, which are com-
posed of resistance coils, or by inserting resistances of low capacity
(ordinary resistance coils) both between the terminals of the instrument
and the real and artificial lines; Figures 1 and 2 show this. If the
artificial line be well adjusted a resistance of about 20 ohms will be
suitable with the other portions of the circuit of resistances, as marked
in Figure 2. With receiving instruments wound differentially Figure 3
will be the arrangement.

page_text: Second. By increasing the capacity of either the receiving instrument
itself or the portions of the circuits with which it is immediately con-
nected. The capacity of the coils of the instrument is increased by
winding them with a wire or conductor having great capacity; to this
5 end I use ordinary wire covered with silk, and afterwards with a very
thin metallic band lapped around it in a close spiral; or I wrap a sheet
of conducting material round each layer of ordinary insulated wire
without the metallic covering; or according to another method I apply
a condenser of small capacity connected on either side of the receiving
) instrument. Figure 4 shows a suitable arrangement. A condenser of
about 2 microfarads will be found sufficient if the compensating circuit
or artificial line be accurately adjusted.
Another method consists in constructing the two sides of the bridge
(see A, B, A, C, Figures 1, 2, and 4) in such a manner as to have
3 capacity to receive a charge; this may be done by winding the resistances
composing the bridge (or a portion of them) with wire covered in the
manner above described. The capacity required is not large; a few
microfarads will suffice if the imitation circuit or artificial line be in
good order.
Another method which I find useful in eliminating disturbances or
"kicks" in duplex working of cables with insufficient or imperfect
apparatus composing the balance or artificial line is to introduce a con-
denser of small capacity with variable high resistance box at a point
in the artificial circuit, which is best ascertained by trial. The arrange-
3 ment is shown in Figure 3 at x.
In cases where the main line is faulty I introduce leakage circuits
through regulated resistances into the artificial line. The arrangement
is indicated in Figure 4 at x, a point depending on the position of the
fault or the resultant fault of the main line.
The above methods are for the most part also applicable to other
systems of "duplex" working, as for example, thoso in which the
receiving instruments are used differentially. Two or more of them
may also be used in combination.
When, as in the method generally adopted for working long cables,
the conductor of the cable is insulated at both ends with condensers, the
conductor of the artificial line for duplex working is also insulated in a

page_text: similar manner, but I find it more economical to leave the distant end
of the conductor of the artificial line free and to place a smaller condenser
(say of about one-third of the capacity of the condensers at the near
end) at a point intermediate of the length of the artificial line. The
proper point is easily ascertained by trial. The arrangement is shewn at
Figure 5. This constitutes another part of my Invention.
Another analogous method is as follows:-In Figure 6 P is tho
primary wire of an induction coil and S the secondary. The secondary S
' is made to be a shunt to the recorder. Any slight disturbance due to
small error of balance is neutralized by the induced current in the
secondary circuit.
As it is of great importance that the first portion of the artificial line
should accurately resemble the first portion of the main line, I in some
cases effect and maintain more effectually the balance between the main
line and the cable by making the first part of the two lines exactly the
same by placing a short length of the artificial line before the cable.
This also prevents disturbance of balance from difference of variation of
the real and artificial lines for temperature.
.
Another convenient arrangement is that indicated in Figure 7. To
move one terminal of the galvanometer or recorder y down the artificial
line a short distance, the point y is determined by experiment; the
first box of the artificial line should be finely subdivided to admit of
this adjustment.
According to the last part of my Invention instead of placing a con-
denser between the receiving instrument and the earth in ordinary
working I prefer to insert a coil of high resistance and great capacity.
Such a resistance may be made of the wire described above. In this
method permanent connection is made between the instrument and the
earth through this high resistance.
I claim the methods substantially as described of constructing
artificial lines suitable for use in duplex telegraphy.
I also claim the methods substantially as described of eliminating the
disturbances or "kicks," which heretofore have been found to occur in
duplex working.
I also claim the method substantially as described of working the
artificial line when the main line is connected at both ends with
condensers.

page_text: I also claim the means substantially as described for substituting in
ordinary working a coil of high resistance and great capacity for a
condenser.
In witness whereof, I, the said John Muirhead, junior, have here-
unto set my hand and seal, this Twenty-seventh day of March,
in the year of our Lord One thousand eight hundred and
.seventy-six.