IMPROVEMENTS IN DUPLEX AND QUADRUPLEX TELEGRAPHY
Year: 1878

page_text: LETTERS PATENT to John Muirhoad, junior, of 29, Regency Street, in the City
of Westminster, for the Invention of "IMPROVEMENTS IN DUPLEX AND
QUADRUPLEX TELEGRAPHY." A communication from abroad by Alexander
Muirhead, James Alfred Briggs, and George Kift Winter, all at present resident
in Madras, in the Empire of India.
PROVISIONAL SPECIFICATION left by the said John Muirhead
at
the
Offico of the Commissioners of Patents on the 12th Novembor 1878.
JOHN MUIRHEAD, junior, of 29, Regency Street, in the City of Westminster.
"IMPROVEMENTS IN DUPLEX AND QUADRUPLEX TELEGRAPHY." [A communication
from abroad by Alexander Muirhead, James A. Briggs, and Georgo Kift Winter,
all at present resident in Madras, in the Empire of India.]
This Invention has for its object improvements in duplex and quadruplex
telegraphy.
In duplex telegraphy I place the battery between the true and artificial lines,
and connect the receiving apparatus between the middle of the battery and earth.
Or the receiving instrument may, in some cases, conveniently be placed nearer the
end of the battery, joined to the artifical line instead of the middle. When I sond
a signal, I short circuit the battery by means of a key. Or I reverse the battery
by a reversing key; thus, supposing copper to be connected to the true, and zinc to
the artificial line, while the key is at rest, the depression of the key joins zinc to
In this latter case, the true and artificial
the true, and copper to the artificial line.
lines must be equal in resistance, and the receiving instruments joined between the
middle of the battery and earth.

page_text: These bars, and consequently the cores of the electro-magnets, are polarized by
being screwed, each of them, to one end of the polarizing magnets c, c. These
magnets, after being bent twice at right angles underneath the bed of the instru-
ment, rise again in the middle at d, d, where they are divided into two jaws by a
slot, between which jaws are pivotted the staffs of the tongues. These tongues
play between the pole pieces of the electro-magnets, and prolongations of them play
between the insulating and central points in the ordinary way.
Figure 2. The section through A, B, shows the arrangement of the tongues.
The arrangement of the contact points of the double tongues is shown in the
section through C, D (Figure 3). In this Figuro, the ends of the tongues are shown
in three positions, 1, 2, and 3, which represent their positions when the currents are
as below.
It will be seen that in only the second position is the connection between contact
point and contact point completed by the tongues. In the 1st and 3rd positions
one tongue is always against an insulated stud, and the connection between point
and point broken. The single tongue works in the ordinary way and needs no
description.
The arrangement of the polarizing magnets will be understood from the section
through E, F, (Figure 4).
A modification may be made by causing the relay, when contact is complete, to
short circuit the local battery, and thus prevent the Morse from working.
To duplex the double sending or biplex system, the nature of which I have
described, the relay or relays may be wound differentially, and the ordinary
differential system used, or, if the bridge systein be used, the wires forming the
branches of the bridge may be wound in opposite directions on an electro-magnet
so that the bridge wires may forin an electro-magnetic shunt for received signals,
but the electro-magnet may be unaffected by the sending currents, or, lastly and
preferably, the split battery system, already referred to, may be adapted to duplex
the arrangement.
There are two ways of accomplishing this:-
1st. I use a reversing key between the ends of the battery, and the true and
artificial lines for one key, and a short circuiting key, cutting off, say, two thirds of
the battery for the other.
2nd. Or I use two reversing keys, one as before between the ends of the battery
and the true and artificial lines, and the other dividing the battery into two por-
tions, this latter key only reversing, say, about one third of the battery. In any
case the receiving apparatus is placed between the middle of the battery and earth.
It is very essential that the reversal of current should be as rapid as possible,
and as on long lines the tendency of the capacity of the wires is to cause a retarda-
tion in this reversal, it is necessary on such lines to adopt the following plans to
counteract as far as possible this retardation.
I connect across the reversing key, between the true and artificial lines, a wire
forming the coils of an electro-magnet.
Or I connect the wires of a second electro-magnet as a shunt on the relay or
relays.
In order to facilitate the adjustment of balance, one or more cells may be placed
between the two halves of the split battery and these colls shunted by a slide
resistance.
The relay will then be joined between the sliding contact and earth.
During the adjustment of balance a galvanometer may be connected between the
sliding contact and the relay, and cut out when the adjustment is complete by
means of a short circuiting plug or equivalent device.

page_text: The adjustment may be made by altering the artificial line as well as by the
sliding contact. It may be convenient to adjust the balance when one key is
worked by altering the artificial line, and when the other key is worked by altering
the slide. This may be found useful when the batteries are not of uniform
strength.
In all cases in which any receiving instrument is used in addition to the rolay,
such as when a Wheatstone's automatic apparatus is used for the reversing side, it
is preferred that the coils of such instrument should be connected in parallel arc
with the relay.

page_text: "
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Muirhead in the Great Seal Patent Office on the 12th
May 1879.
John Muirhead, junior, of 29, Regency Street, in the City of Westminster.
IMPROVEMENTS IN DUPLEX AND QUADRUPLEX TELEGRAPHY." (A communication
from abroad by Alexander Muirhead, James Alfred Briggs, and George Kift Winter,
all at present resident at Madras, in the Empire of India).
This Invention has for its object improvements in duplex and quadruplex
telegraphy.
The improvements in duplex telegraphy consist in placing the battery between
the true and artificial lines, and connecting the receiving apparatus between the
middle of the battery and earth. In order to give a signal the battery is reversed.
Thus supposing copper to be connected to, the true, and zinc to the artificial line,
while the key is at rest, the depression of the key will join zinc to the true and
copper to the artificial line.
In this arrangement perfect balance is obtained when the true and artificial lines
are equal, and balance is perfectly independent of any changes in the resistance and
electro motive forces of the two halves of the battery, any inequality in which will
merely cause a current to flow through the receiving instrument, but which current
will remain the same whether a signal is being sent or not, that is, whether the
battery is direct or reversed. The arrangement will be understood from Figure 1.
In the reversing keys the continuous lines represent the connections when the keys
are at rest, and the dotted lines those when the keys are depressod. These reversing
keys may be of ordinary and well known construction.
It will be seen that as far as the receiving instrument and batteries are concerned
it is really the true and artificial lines which are affected by the reversing key.
They mutually replace one another in two portions of the circuit external to the
instrument and batteries. There has therefore been given the name of double sub-
stitution to this form of duplex working, which, although similar in appearance to
the split battery system, differs from it essentially in principle, for whereas in the
split battery system balance depends on the maintenance of a strict proportion
between the electro motive forces of the two halves of the battery and the
resistance of the true and artificial lines, the balance in the method of double
substitution depends only on the equality of the true and artificial lines, which,
however, experience shows may differ widely without effecting the received signals
injuriously.
"The principal merits claimed for this plan are,
1. Its very wide working range. The artificial line may be altered within wide
limits without affecting the signals.
2. The fact that tho plan requires no special winding of the coils as in the
differential system.
3. That the sensitiveness of the relay is not reduced, and magnetic retardation
increased by the shunting action of bridgo wires, as in the bridge span.
4. The balance, as stated above, is not disturbed by variations in the electro
motive forces or resistances of the two halves of the battery, as is the case in the
ordinary split battery system, that is, when the battery is cut out of circuit by a
short circuiting key, or the two holes of the battery put simultaneously into and out
of circuit according to Heavyside's plan. In addition to this, the action of the
signalling on the distant instrument is of course doubled.
All that is necessary to neutralize any current which may be passing through
the receiving instrument in consequence of inequality in the two halves of the
battery is to join the receiving instrument slightly out of the centre of the battery.
In order to do this effectually I may shunt two or more of the middle cells of the
battery by a slide resistance equal to about three or four times the resistance of the

page_text: after described.
At the receiving station there is a polarized relay adjusted to break the local
circuit when the current is plus, and to complete it whenever the curront becomes
minus; a local sounder or other receiver connected with this relay records the
depressions of key A.
There is also in the main current at the receiving station a double tongued relay,
which is used for completing the circuit of the sounder or receiver intended to
respond to the movements of the key B.
This double relay, which forms an important feature of the Invention, is so
arranged that in order that the local circuit should be completed, it is necessary for
both tongues to be against their respective contact points. To accomplish this either
the tongues are insulated and the contact between tongue and tongue caused to be
completed through the contact points, which in this case are connected electrically
with each other, or the contact points are insulated and the contact between point
and point is completed through the tongues, which in this latter case are of course
connected together.
3.
The polarity and adjustment of the tongues is so arranged that the contact
between one tongue and its point is only broken when the current is + 3, and that
between the other tongue and its point is only broken when the current is
With the intermediate strengths of 1 and
+
both tongues are in contact with
their points, and the circuit of the relay is complete. Thus the local circuit is
broken when the current is either
3, but it is closed when the current is
either + 1 or 1.
-
+
3 or
-
Both the contact points are fixed to the same carrier, and things are so arranged
that when once the contact points have been individually adjusted their further
adjustment for ordinary changes in strength of the currents is made simultaneously
by one and the same motion of the carrier.
On very long lines it may be necessary to use a local relay to work the recorder,
the local circuit of this second relay being completed by the relay I have described,
but this will not be generally necessary.
Figures 3 and 4 represent respectively a plan and section of one form of the
double relay. In this form both tongues C, C, play between the same pole picces
A, A, of the electro magnets B, B. The tongues are polarized oppositely by a per-
manent magnet D, D, D, so arranged that one end of it polarizes the upper tongue
and the other end polarizes the lower tongue.
The electro magnets are placed horizontally one on each side of the tongues, and
at right angles to them. The pole pieces A, A, of the electro magnets are flat pieces

page_text: of soft iron of the same width as the core, and continued vertically above and
below the cores across the flanges sufficiently far to envelope both tongues in their
action. The tongues are caused to play as nearly as possible at equal distances
above and below the axes of the cores, so that the action on them may be as uniform
as possible. The contact points are on the same side of the carrier, and one
above the other. They are insulated from the frame work of the relay and from
each other, contact between then being completed through the tongues when both
tongues are against their respective contact points.
The three positions of the tongues, corresponding with the currents + 3, +1
(B depressed), and 3 respectively, are shown in Figure 5.
After the first adjustment of the tongues their further adjustment is made by
moving the whole carrier e, e, by means of tho slow motion screw f, f, which works
in a nut underneath the carrier.
It is evident that the action of any current passing through the coils of the electro-
magnets is to cause the electro-magnets to act oppositely on the upper and lower
tongues in consequence of the opposite polarity; thus, if a plus current tonds to
cause the upper tongue to move in the direction of its insulated point a minus
current will have the saine effect on the lower one. The adjustment of the tongues
is such that it requires a strength of +3 to act thus upon the upper tongue, and
3 to act in the same way on the lower tongue. If the current has either of the
intermediate strengths of +1 or 1, the strength is insufficient to move either
of them against the bias given them against their contact points, and consequently
both tongues are in contact with their respective contact points, and the local
circuit of the relay is complete. When the current changes rapidly from + 3 to
-
-
3, the lower tongue leaves its contact point before the upper tongue has time to
make contact. It is only when this change is retarded that any difficulty is
experienced in working the local instrument B direct with this relay. If the
instrument is a recorder the signals are perfect, as the effect of retardation is only
to cause a slight trembling of the armaturo against its upper limiting stop, and is
insufficient to affect the record. With sounders there is an inconvenience which
can be remedied by using an extra local relay to complete the circuit of the
sounder, the local circuit through the coils of which extra relay being completed by
the double relay I have described. This arrangement will probably only be found
necessary on very long lines, or where any considerable length is submarine or
subterranean.
Another form of double relay, which has been found to bo equally good, and in
some respects inore convenient, is shown in Figures 6 and 7.
In this form the tongues C, C, aro polarized in the same sonse by the permanent
magnet D, D. The tongues in this form are insulated from the frame work of tho
relay and from each other, and contact between them is established when both
tongues are against their respective contact points, which, as in the former case, are
fixed to the same carrier and the same side of it, but they are uninsulated. The
electro-magnets E, E, E, E, are in this case polarized by the ends of the two perina-
nent magnets D, D, the other poles of which polarize the tongues, so that all four
cores and pole pieces have the opposite polarity to that of the tongues C, C, which
play between them. The action of the currents on the tongues is in this case
precisely similar to that which I have already explained in reference to the other
form of relay. In this case however the polarity of the two tongues is the same,
but the polarities of the pole picces between which they play are effected by the
current in opposite sense, and consequently opposite motions result in the tongues
as in the former case.
I will now explain how the double sending or biplex system is duplexed.
I apply the method of double substitution, which in its simple form I have already
described.
This may be done in either of two ways,
1st The batteries and keys may be inined as shown in Figure 8.

page_text: keys. By closing the key B or B₁ the battery is reduced from 3 n cells to n cells.
By pressing the reversing key A or A¹ the battery, whether of the power of n or
3 cells, is simply reversed. The relays are placed between the middle of the
battery and earth.
2nd. The batteries may be joined up with two reversing keys at B, B₁, as in
Figure 9.
3 2.
In this arrangement the keys B and B separate the batteries into two portions,
of one which one contains 2 n cells, and the others cells. When these keys are
at rest the connections are along the continuous lines, and the two portions of the
batteries are acting in the same direction, so that the current is 2n + n =
When these keys are depressed they reverse n cells of the battery, so that there are
only 2 n 22 = cells acting. The keys A and A', when depressed, simply reverse
the current, whether it is 3 n or only n as before.
The mechanical construction of the keys (which are such as are well known as
reversing keys), and the detail of these connections is shown by Figure 9.
Although these plans have only been described as giving the ratio + 3 to + 1 as
the battery powers employed, yet it is obvious that by changing the position of the
keys B, B, the ratios may in either plan be altered as desired.
Where there is a want of uniformity in the batteries balance may be perfect for
key A, but imperfect for key B.
When key B is a short circuiting key this may be remedied in the following way,
sco Figure 10.
A few cells may be placed between the two halves of the battery and these cells
shunted by a slight resistance. It is evident that the adjustments of this slide will
not affect the balance as far as key A is concerned, but it will affect the balance for
key B; in practice therefore the artificial line is first adjusted to obtain balanco
when key A is worked, and the balance for key B is then adjusted by means of the
slide.
When key B is a reversing key matters are arranged as in Figure 11. Two
resistances, are inserted as shown in the Figure. It is evident that the altera-
tion of these resistances will not affect the balance as far as key A is concerned,
but it will affect the balance when key B is worked, as their resistances are external
to this key. The artificial line is therefore first adjusted to obtain balance when
key A is worked, and the resistances r, 7, are then adjusted, so as to obtain
balance when key B is worked. These resistances may be conveniently arranged,
so that one is increased and the other decreased, and vice versa, simultaneously.
These arrangements will not be found generally necessary, but they are useful as
a precautionary measure in case the batteries get into bad order.
It is of course very essential that the reversal of current through the double
relay should be as rapid as possible, and as on long lines the tendency of the
capacity of the wires is to cause a retardation in this reversal, it is advisable on
such lines to adopt the following plans to counteract, as far as possible, the effect of
this retardation.
1st. Connection may be made across the reversing key A, between the true and
artificial lines the wire forming the coils of an electro magnet, as shown at C in
Figure 12.
2nd. The wires of a second electro-magnet may be connected as a shunt on the
double tongued relay, as shown at D in Figure 12. It is advisablo that the resist.-
ance of the electro magnet at C should be at least equal to twice that of the line,
and that at D at least equal to that of the relay it shunts. The electro magnets
may be of the closed horse shoe form, as shown in section in Figure 13.
Or they
may consist of a single rod of soft iron, with flanges also of soft iron, and a cylin-
drical casing of iron closing over the wire, and connecting magnetically flange with
Hange, as shown in section in Figure 14.
When it is necessary to compensate for static induction it is preferred to use
Muirhead's inductive resistance for the artificial line.
By carrying on the same principle further the quadruplex arrangement may be

page_text: added to and made multiplex, thus, for instance, in triplex telegraphy, which
may be duplexed, three keys are employed, and the currents are arranged as
follows:-
:-
-
Let, A, b, B, C, C, represent the three keys, the small letters meaning that
the key is at rest, and the capital letters that the key is depressed; then currents
The recorders corresponding with A and B are worked as in biplex telegraphy,
while that corresponding with C is worked with two double tongued relays, or one
relay with four tongues, which is better. Two tongues complete the local circuit
between + 5 and 5, the other two tongues short circuit the recorder at +1
and 1. Or one pair of tongues may close or open the circuit between + 5 and
+3, and the other pair may close or open it between 3 and 5. In either case
a relay acted on by the local circuit of this compound relay is required to work the
recorder. It is of importance that the electro magnets in the double or quadruplex
tongued relays should be sinall.
1
Having thus described the nature of the said Invention, and the manner of
performing the same, I would have it understood that I claim,-
First. The method of duplex telegraphy (or telegraphy with simultaneous trans-
mission in opposite directions) consisting in inserting the battery between the true
and the artificial lines, and the receiving apparatus between an intermediate point
in the battery and the earth, the signals being made by a reversing key crossing the
connections of the true and artificial line, substantially as described.
Second. The method of duplex telegraphy, consisting in inserting the battery
between the true and the artificial lines, and the receiving apparatus between an
intermediate point in the battery and the earth, the signals being made by a key
short circuiting the battery, substantially as described.
Third. The method of working two messages simultaneously in the samo direction,
consisting in employing transmitting keys, which alter both the strength and the
sign of the current, and two sets of receiving apparatus, the one set comprising a
polarized relay, which completes a local circuit when the sign of current is changed,
and the other a double tongued relay, which completes a local circuit when the
line current is of a certain strength whatever be its sign, substantially as
described.
Fourth. The construction of the double tongued relay, substantially as described.
Fifth. The method of quadruplex telegraphy by the combination of the heroin
described duplex and biplex arrangements, substantially as described.
Sixth. The several improvements in duplex and quadruplex telegraphy, substan-
tially as herein described, and illustrated by the annexed Drawings.
In witness whereof, I, the said John Muirhead, junior, have hereunto set my
hand and seal, this Tenth day of May, in the year of our Lord One thousand
eight hundred and seventy nino.
J. MUIRHEAD, JR. (L.S.)