AN IMPROVED ELECTRICAL COMMUTATOR, TOGETHER WITH THE APPLICATIONS OF THE SAME
Year: 1874

page_text: LETTERS PATENT to Alexander Melville Clark, of 53, Chancery Lane,
in the County of Middlesex, Patent Agent, for the Invention of
"AN IMPROVED ELECTRICAL COMMUTATOR, TOGETHER WITH THE APPLICATIONS
OF THE SAME." -A communication from abroad by Henry Lartiguo,
of Paris, France.
Sealed the 13th April 1875, and dated the 31st October/1874.
PROVISIONAL SPECIFICATION left by the said Alexander Melville
Clark at the Office of the Commissioners of Patents, with his.
Petition, on the 31st October 1874.
I, ALEXANDER MELVILLE CLARK, of 53, Chancery Lane, in the County
of Middlesex, Patent Agent, do hereby declare the nature of the said
Invention for "AN IMPROVED ELECTRICAL COmmutator, TOGETHER WITH THE
APPLICATIONS OF THE SAME," to be as follows:
-
The improved commutator of this Invention is designed to utilize the
electrical conducting power of mercury as well as its fluidity for
establishing electrical communications under certain conditions, whether

page_text: as regards the duration and the automatic interruption of the circuits, or
in respect of the direction or inversion of the currents.
Figures 1, 2, 3, and 4 of the accompanying Drawings show one
example of an apparatus of this nature, although many different com-
binations may be made to suit the purpose to which it is to be applied.
A is a chamber made of some insulating material, such as ebonite
hermetically closed and divided into two compartments L, l, of unequal
size, by a partition, the two compartments communicating by an orifice O
at the lower part of the partition, and a smaller orifice E at top of same.
Two wires of platinum or steel f, f', arc introduced in the larger com-
partment near the partition and at the upper and lower parts respectively,
and the chamber contains one-third of its capacity of purified mercury.
When the box is horizontal, as in Figure 1, the mercury occupies
the lower part of each compartment and covers the lower wire f. By
suddenly tilting the box in the direction shown in Figure 3 the mercury
will risc on the side N and so cover the upper wire f¹, thus establishing
communication between the wires; should the box remain thus inclined
the mercury will flow through the lower aperture O from the large into
the small compartment to the level indicated by the dotted linen, n,
and uncover the upper wire, thus automatically interrupting the circuit
after a longer or shorter period of time, according to the quantity of
mercury and the size of the orifice O. The upper orifice E allows the
air displaced by the mercury to pass from the small compartment to the
other. Thus it will be seen that with such an arrangement the following
results are obtained, viz. :-
1st. When the box is horizontal, as in Figure 1, the wires f, f¹, are
insulated the one from the other.
2ndly. When the box is suddenly tilted communication is established
between the two wires, as in Figure 3.
Brdly. If the box be slowly tilted the wires will still remain discon-
nected, the mercury flowing from one compartment to the other without
rising up the partition or reaching the upper wire f¹.
4thly. If the box after having been suddenly tilted is allowed to
remain in that position the circuit will be broken automatically after a

page_text: 5thly. If the box is inclined in the reverse direction, as in Figure 4,
the wires will remain unconnected.
6thly. The contacts are protected from external influences, while by
employing insulated wire connections the apparatus may be made to act
under water or other liquids which are conductors of electricity. To
avoid oxidation of the wires contained in the box they may if preferred
be kept constantly immersed in mercury contained in separate channels,
as shown in Figure 5, communication being in that case established
between the one portion of the mercury and the other portion. It
should be remarked that the contact with the wires is made by mercury
in movement and by the under layers of the fluid, so that all objections
due to the alteration of the surface of the mercury or to deposits which
are liable to prevent electrical contact when a wire is brought only
superficially in contact with such surface are avoided.
Figure 6 shows the method of connecting the conducting wires with
those of the box. The latter passes through nipples formed on the box,
and the joint is made and covered with an insulating coating and the
whole enclosed in a rubber tube firmly attached to the socket on the
box. In this manner perfect insulation is obtained. When using boxes
of ebonite it would be of advantage to varnish the interior to protect the
mercury from the action of the sulphur employed in the manufacture of
this material.
It should be understood that this Invention does not apply to a prior
arrangement in which electrical communication is established between
two compartments of a movable box containing mercury by means of an
aperture. In the improved commutator of the present Invention the
aperture in the partition serves solely to allow the fluid to flow from one
compartment of the box to the other (as in a clepsydra, and as shown in
the Drawing) in order to vary the level and regulate the time of
contact.
The apparatus may be made of the form shown in Figure 8 and one of
the compartments be dispensed with, as in Figures 7 and 8, or the
number may be increased, as in Figure 12, or lastly they may be quite
separate one from the other, the communicating apertures being
dispensed with, as in Figures 9, 10, and 11.
The following are some of the applications of the improved com-
mutator of this Invention :-
1st. As annlied to the breaks of winches or the regulators of hoiste ·

page_text: and other similar machines operated by electricity, see Figure 13. The
commutator A is fixed on a lever B, one arm of which is provided with
a spring blade C or equivalent device, and is oscillated by the passage of
a weight or other body D. The mercury box first described is used in
this case if it is desired that the circuit should be of short duration even
although the balance lever should remain inclined, as also when it is
required that the circuit should only be made upon a movement of pre-
determined rapidity taking place. If on the other hand it is simply
desired to make electrical contact the arrangement of box, Figure 7, with
a single compartment is used, but the contact will not in any case be
effected by the movement of part D when that movement is the reverse-
of that required to close the circuit.
2ndly. As applied for indicating the level of liquid in a vat or other
container (see Figure 14). The oscillating lover B is provided with a
funnel E at one end disposed beneath a nozzle F placed at the level to
be indicated, and when this level is reached the liquid flows from the
nozzle into the funnel and oscillates the apparatus. When the funnel
has discharged its contents it will resume its horizontal position.
3rdly. When the Invention is applied for the purpose of indicating
sudden changes of pressure in pipes or reservoirs of liquids and gases,.
apparatus such as those of the first two arrangements are employed but
modified to suit the conditions required. All gradual variations of
pressure whatever may be their extent are not indicated by the apparatus
but only sudden variations.
Spring plates H are
4thly. Figures 15, 16, and 17 show the Invention adapted to alarm
apparatus at railway level crossings and tunnels in connection with a
lever to be operated by the passage of a train. The rock lever B is in
this case carried on a sleeper G inside the rail.
attached to this lever so as to be acted on by the flange of the wheel for
rocking the lever. To prevent violent shocks a spring blade I is placed
horizontally beneath spring H with a rubber cushion J interposed
between them, secured by check plates K.
.
5thly. Figures 18 and 19 show the Invention as applied to torpedoes
where the circuit is closed by a shock or a sudden variation of the level
in any direction. The commutator A in this case assumes the form of
a cylinder having two compartments disposed concentrically. One wire
is placed at the bottom while the other runs round the sides of the

page_text: central compartment at about two-thirds of its height. A number of
orifices in various directions serve to connect the two compartments
together. The action is the same as in the first arrangement described
except that it takes place whichever way the apparatus is inclined. The
arrangement is applicable to those submarine torpedoes in which the
electric circuit is to be made automatically by the blow of a vessel's hull
in passing over it although the oscillation produced by the motion of the
waves will have no such effect, and it may be used as a substitute for
the arrangement at present in use which consists of a sphere mounted
on a flexible stem and which strikes contacts disposed around the casing.
By the present Invention insulation in sea water is more easily effected
and the apparatus is less expensive. The above arrangement may also
be used for indicating when a moving body, a fly wheel for example, is
running at too high a velocity or has suddenly stopped.
6thly. Figures 20 and 21 show the Invention as applied for controlling
the working of railway switches. Outside the rail L and opposite the
toe of each switch rail M an arm N is pivoted at O, to which arm is
jointed a rod P which works through a slot in the stock rail and projects:
slightly on the opposite side to an extent regulated by a set screw.
When the switch rail M is home against the stock rail the stem P is
forced back, thereby raising rock lever N, and with it the commutator A
fixed thereon; but if on the contrary the switch rail is not brought
home close against the stock rail the rock lever N assumes a somewhat
horizontal position. Thus in the normal position of the switch one of
the commutators will be horizontal and the other inclined, as shown,
while if the switch is left partly open both commutators will remain in
a horizontal position, as shown in Figure 22. If it is simply desired to
control the working, that is to say, merely to show that the switch rail
is brought home against the stock rail, the position of the switch being
sufficiently indicated by that of the switch lever, the apparatus
would be arranged as in Figures 20, 21, and 22, that is to say, with two
contacts, both placed near the bottom of each box A, the contacts next
the partitions in the two boxes being connected together by a wire. The
second contact of one of the boxes is connected with a battery R, while
the corresponding contact of the other box connects with a bell-sounding
apparatus S contiguous to the switch lever. The parts being thus
arranged, every time of working the switch a circuit is established and
the bell continues to sound until the mercury leaves the second contact

page_text: exposed, and if both switch rails should remain away from their stock
rails the bell will continue to sound to give warning that the switch is
not in its proper position. The proper working of the electric apparatus
is also shown by the bell which should sound immediately at each time
of working. If in addition to indicating the proper working of the
switch it is desired to know the direction in which it is moved a third
contact is disposed at the upper part of the larger compartment of each
box, the wires being arranged, as shown in Figures 23, 24, and 25, and
a galvanometer T giving a permanent record is interposed, as shown, to
indicate the direction of the switch by means of a needle. The bell
mechanism acts in the same manner as before.
7thly. By means of an arrangement similar to the foregoing,
employing either a single rock arm or two combined, the Invention
may be applied for controlling the position of railway or other signals,
doors, windows, bolts, and other similar purposes.
8thly. The Invention may be applied for reversing electric currents.
Figures 9, 10, 11, and 12 show several arrangements of the commutator
for this purpose. The mercury compartments are entirely separate one
from the other, being connected by the wires only, in the case of an
ordinary permanent reverser, as in Figures 9, 10, and 11, or if it is to be
used for reversing and afterwards automatically interrupting the circuit
the mercury box would be divided into four compartments connected
together two-and-two by openings, as in Figure 12.
From the foregoing it will be seen that the improved commutator of
this Invention may be used either for establishing a permanent circuit
or an intermittent circuit which is automatically interrupted, or for
sending currents in different directions by simply imparting a rocking
motion to the apparatus in any suitable manner. Morcover as the
mercury box is hermetically closed and the wires are protected by an
insulating covering the apparatus may be used in any situation, the
contacts and connections being entirely free from liability to derivations.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Alexander Melville Clark in the Great Seal Patent
Office on the 29th April 1875.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, ALEXANDER
MELVILLE CLARK, of 53, Chancery Lane, in the County of Middlesex,
Patent Agent, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Thirty-first day of October, in the year
of our Lord One thousand eight hundred and seventy-four, in the thirty-
eighth year of Her reign, did, for Herself, Her heirs and successors,
give and grant unto me, the said Alexander Melville Clark, Her special
licence, that I, the said Alexander Melville Clark, my executors,
administrators, and assigns, or such others as I, the said Alexander
Melville Clark, 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, excrcise, and vend, within the United Kingdom of Great
Britain and Ireland, the Channel Islands, and Isle of Man, an Invention
for "AN IMPROVED ELECTRICAL COMMUTATOE, TOGETHER WITH THE APPLICATION
OF THE SAME,' a communication to me from abroad by Henry Lartigue,
of Paris, France, upon the condition (amongst others) that I, the
said Alexander Melville Clark, my executors or administrators, by
an instrument in writing under my, or their, or one of their hands and
seals, 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 Alexander Melville Clark, 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, reference being had to the
two Sheets of Drawings hereunto annexed and to the letters and figures
marked thereon, that is to say :—
The improved commutator of this Invention is designed to utilize the
electrical conducting power of mercury as well as its fluid property

page_text: for establishing clectrical communications under certain conditions,
whether as regards the duration and the automatic interruption of the
circuits, or in respect of the direction or inversion of the currents.
"
Two
Figures 1, 2, 3, and 4 of the accompanying Drawings show an apparatus
of this kind, but many different combinations may be made to suit
particular purposes, although the one shown will explain the object
sought to be attained and the means employed for the purpose. A is a
box made of some insulating material, such as ebonite, hermetically
closed and divided into two compartments L, 7, of unequal size by a
partition, the two compartments communicating by an orifice o at the
lower part of the partition and a smaller orifice E at top of same.
wires of platinum or steel f, fs, arc introduced in the larger compartment
near the partition, the one being near the bottom and the other about
two-thirds the height of the chamber, and the box contains about one-
third of its capacity of purified mercury. When the box is horizontal,
as in Figure 1, the mercury occupies the lower part of each compartment
and covers the lower wire f. By suddenly tilting the box in the direction
shown in Figure 3 the mercury will risc against the partition, as at N,
and cover the upper wire f¹, thus establishing clectrical communication
between the two wires. Should the box remain thus inclined the
mercury will flow through the lower aperture o from the larger into the
smaller compartment to the level indicated by the dotted linen, n, and
uncover the upper wire, thus automatically interrupting the circuit after
a longer or shorter period of time, according to the quantity of mercury
and the size of the orifice o. The upper orifice E allows the air displaced
by the mercury to pass from the one compartment to the other in the
opposite direction to the mercury. It will now be seen that with such
an arrangement the following results are obtained, viz. :—
First. When the box is horizontal, as in Figure 1, the wires ff', are
insulated the one from the other.
Secondly. When the box is tilted suddenly communication is established
between these wires, as in Figure 3.
Thirdly. If the box be slowly tilted the wires will still remain
electrically disconnected, the mercury flowing from one compartment
to the other without rising up the partition or reaching the upper
wire f¹.
Fourthly. If the box after haying been suddenly tilted is allowed to

page_text: remain in that position the circuit will be broken automatically after a
certain lapse of time, which may be accurately determined by regulating
the size of the orifice o.
Fifthly. If the box is inclined in the reverse direction, as in Figure 4,
no communication will be established.
Sixthly. The contacts are protected from external influences, while by
employing insulated wire connections the apparatus may be made to act
under water or other liquid which is a conductor of electricity. To
avoid oxidation of the wires contained in the box they may if preferred
be kept constantly immersed in mercury contained in separate channels,
as shown in Figure 5, communication being in that casc established
between the one portion of the mercury and the other portion. It should
however be remarked that the contact with the wires is always made by
the mercury in a state of agitation, and by the under layers of the fluid,
thereby avoiding all objections arising from the alteration of the surface
of the mercury or the deposit of solid matter thereon, which might
prevent electrical contact if the wires were brought only superficially in
contact with the mercury.
Figure 6 shows the method of connecting the external conducting
wires with those of the box. The latter wires pass through nipples
formed on the box, and the connection is made and covered with an
insulating coating, and the whole enclosed in a rubber tube firmly
attached to the nipple on the box. In this manner perfect insulation is
obtained. When using boxes of cbonite it would be of advantage to
varnish the interior to protect the mercury from the action of the sulphur
employed in the manufacture of this material.
This Invention is quite distinct from one already proposed, in which
electrical communication is established between two compartments of a
movable box containing mercury by means of an aperture. In the
improved commutator of the present Invention the aperture in the
partition simply serves to allow the fluid to flow from one compartment
of the box to the other (as in a clepsydra, and as shewn in the Drawing)
in order to vary the level and regulate the duration of contact.
The above described apparatus serves merely as an example, and as,
before mentioned, is capable of considerable variations to suit the
different applications of the apparatus. The general form of the
apparatus may be modified, as shewn in Figure 8, and the relative sizes

page_text: of the compartments may be varied, and one of the compartments may
be dispensed with entirely, as in Figures 7 and 8. On the other hand
the number of compartments may be increased, as in Figure 12, and
they may be made quite separate one from the other by dispensing with
the communicating apertures, as in Figures 9, 10, and 11.
The following are some of the applications of the improved commu-
tator of this Invention.
Figure 13 shows it as applied to the brakes of winches or to the
regulators of hoists and other similar machines governed by clectricity.
In this example communication is established by the upward or down-
ward passage of a weight or other solid body. The commutator A is
fixed on a lever B, one arm of which is provided with a spring blade C
or equivalent device, and is oscillated by the passage of a weight or
other body D. The mercury box first described is used in this case if it
is desired that the circuit should be of but short duration, even although
the balance lever should remain inclined, as also when it is required that
the circuit should only be closed upon the occurrence of a movement of
a certain pre-determined rapidity taking place. If on the other hand it
is simply desired to make electrical contact the arrangement of box,
Figure 7, with a single compartment is used, but the contact will not in
any case be effected by the movement of part D when that movement is
the reverse of that required to close the circuit.
Figure 14 shows the Invention as applied for indicating the level of
liquid in a vat or other container. The oscillating lever B is provided
with a funnel E at one end, disposed beneath an overflow nozzle F
placed at the level to be indicated, and when this level is reached the
liquid flows through the nozzle into the funnel and oscillates the appa-
ratus. When the funnel has discharged its contents it will resume its
horizontal position.
In applying the Invention for the purpose of indicating sudden
changes of pressure in pipes or reservoirs of liquids and gases, apparatus
such as those used in the first two applications mentioned are employed,
but modified to suit the conditions required. All gradual variations of
pressure, whatever may be their extent, are not indicated by the appa-
ratus, but only sudden variations.
Figures 15, 16, and 17, show the Invention adapted to alarm apparatus
et loval nunssives and tunnels (for instancat on Mail A

page_text: The rock lever B
Spring plates H
with a lever to be operated by the passage of a train.
is in this case carried on a sleeper G inside the rail.
are attached to this lever so as to be acted on by the flange of the wheel
for rocking lever. To prevent violent shocks a spring blade I is
placed horizontally beneath spring H with a rubber cushion J interposed
between them, secured by side plates K.
Figures 18 and 19 show the Invention as applied to torpedoes, whero
the circuit is closed by a shock or a sudden inclination of the apparatus in
any direction. The commutator A in this case is in the form of a
cylinder having two concentric compartments. One wire is placed at
the bottom, while the other runs round the sides of the central com-
partment at about two-thirds of its height. A number of orifices in
various directions serve to connect the two compartments together.
The action is the same as in the first arrangement described, except that
it takes place whichever way the apparatus is inclined. This arrange-
ment is applicable to those submarine torpedoes in which the electric
circuit is to be closed automatically by the hull of the vessel to bo
destroyed striking as it passes over it, although the oscillations pro-
duced by the motion of the waves will have no such effect, and it may
be used as a substitute for the arrangement at present in use, which
consists of a sphere mounted on a flexible stem, and which strikes
contacts disposed around the casing. By the present Invention insu-
lation in sea water is more easily effected and the apparatus is less
expensive. The above arrangement may also be used for indicating
when a moving body, a fly wheel, for example, is running at too high a
velocity or has suddenly stopped.
Figures 20 and 21 show the Invention as applied for controlling the
working of railway switches. Outside the rail L, and opposite the toe
of each switch rail M an arm N is pivoted at o, to which arm is jointed
a rod P which works through a slot in the stock rail and projects slightly
on the opposite side to an extent regulated by a set screw. When the
switch rail M is home against the stock rail the stem P is forced back,
thereby raising rock lever N and with it the commutator A. fixed thereon,
but if on the contrary the switch rail is not brought home close against
the stock rail the rock lever N assumes a somewhat horizontal position.
Thus in the normal position of the switch one of the commutators will
be horizontal and the other inclined, as shown, while if the switch is left

page_text: partly open, both commutators will remain in a horizontal position, as
shown in Figure 22. If it is simply desired to show that the switch rail
is brought quite home against the stock rail (the position of the hand
lever indicating whether the switch is open or closed for the branch line)
the apparatus would be arranged as in Figures 20, 21, and 22, that is to
say, with two contacts, both placed near the bottom of each box A, the
contacts next the partitions in the two boxes being connected together
by a wire. The second contact of one of the boxes is connected with a
battery R, while the corresponding contact of the other box connects
with an alarum S contiguous to the switch hand lover. The parts being
thus arranged, every time the switch is moved a circuit is established
and the bell continues to sound until the mercury leaves the second
contact, and if cither of the switches should fail to be brought home
against its stock rail whilst the other is in the open position, the bell
will continue to sound to give warning that the switch is not in its
proper position. The proper working of the electrical apparatus is also
shown by the bell which should sound immediately at each time of
working the switch. If on the other hand it is desired not only to
indicate that the switch is working properly, but also the position of the
switch, a third contact is disposed at the upper part of the larger com-
partment of cach box, the wires being arranged as shown in Figures 23,
24, and 25, and a galvanometer I giving a permanent record is interposed
as shown, to indicate the direction of the switch by means of a needle.
The bell mechanism acts in the same manner as before.
By means of an arrangement similar to the foregoing, employing
either a single rock arm or two combined, the Invention may be applied
for controlling the position of movable parts, such as railway or other
signals, doors, windows, bolts, and other similar purposes. Thus, for
example, in order to control the working of switches by a different
arrangement to that previously described, that is to say, by adapting the
apparatus to the connecting rod instead of to the switch rail, whereby
but one single mercury commutator is required, I may employ the
arrangement shown in side and front views in Figures 26 and 27, and
plan in Figure 28. In this arrangement A is a metal plate fixed to a
sleeper. X is a pin fixed in plate A on which is hung a rocking plat-
form B with stem H and counterbalance P, which tends to maintain
the horizontality of table B. The latter carries a commutator C having
three compartments communicating with each other by apertures at

page_text: |the lower part and provided with two electrical contacts in the central,
compartment.
When the commutator is in a horizontal position the mercury.
establishes permanently the circuit, in which is an alarum, and on being
inclined to the right or left the circuit is broken when the mercury
ceases to flow into the lower compartment. Thus the alarum continues
to sound at each change of position of the commutator during the
time the mercury is flowing, after which it ceases to sound. On the
connecting rod L of the switches a pair of arms V are attached, as
shown, one or other of said arms coming in contact with weighted arm H,
and inclining the commutator according to the direction in which the
switch is moved. The set screws V₁ on the end of each arm V permit
of regulating the moment of contact of parts V and H, as well as the
degree of oscillation of the commutator, according to the position of the
switch tongues relatively to their stock rails. This arrangement is
applicable in other cases where it may be desired to give warning of any
moving part being in a position intermediate of its two extreme positions.
If, on the other hand, it is desired to check all three positions, as
for example in the case of a railway signal, viz., first, the position indi-
cating "line clear," in which no alarm will be sounded; second, the.
position for "linc blocked," by sounding an alarum at the station; and,
third, an intermediate position owing to the signal not being properly set,
which is indicated by the sounding of a special alarum contiguous to the
hand lever to warn the signalman of the fact. In this case I employ a
commutator having two entirely separate compartments, each provided
with three electric contacts, as shown in Figure 29. In this arrange-
ment it will be seen that the commutator when inclined to the right in
the position A, corresponding to the "line clear" position of the signal,
does not transmit any current, and when in the horizontal position B, as
in the case of the signal being improperly set, a negative current is
transmitted on the line L, while when inclined to the left in the position
C, corresponding to the "danger" or "line blocked" position of the
signal, a positive current is transmitted. A galvanometer G, Figure 30,
is attached to the line wire L, with the needle D of which the other end-
of the coil communicates. To this needle is attached at right angles.
therewith a light bar of steel or platinum T, whose two ends are bent.
downwards and dip into two cups M, M', filled with mercury,
and com-.
municating the one with the station alarum S, and the other with the
alarum L at the signal lever. In the position A, Figure 29, of the.

page_text: commutator, corresponding to "line clear," and in the absence of any
current, the needle D of the galvanometer remains in a vertical position,
and the two bent ends A, A, of bar T both dip into the mercury cups.
Supposing now the signal to be moved, and the commutator to be
brought to the horizontal position B, Figure 29, a negative current is
caused to pass through the coils of the galvanometer, and simultaneously
to both of the alarums, but the needle D being immediately deflected
towards M², and the bar Tassuming the position B, B is raised out of
the mercury cup M, and the whole current is thus transmitted through
the alarum L at the hand lever, which is thereby sounded, and continues
to sound if the signal remains improperly set. If on the other hand the
signal is moved to the "line blocked" position, and the commutator is
inclined to the left, as in position C, Figure 29, needle D will be deflected
in the opposite direction towards trough M, while bar T will assume the
position C, C, and the station alarum alone will be sounded. The signal-
man is thus made aware after each movement whether or not it is
properly performed, while he is also enabled to check at same time the
working of the electric apparatus, which should sound momentarily in
setting the signal; therefore if no sound is heard it shows that the
apparatus is deranged. It is unnecessary to add that other mechanical
movements may be controlled by similar means, the form and arrange-
ment of the parts being adapted to suit each particular case.
The Invention may be applied for reversing electric currents. Figures 9,
10, 11, and 12 show several arrangements of the commutator for this
purpose. The mercury compartments are entirely separate one from the
other, being connected by the wires only in the case of an ordinary
permanent reverser, as in Figures 9, 10, and 11, or if it is to be used for
reversing and afterwards automatically interrupting the circuit the
mercury box would be divided into four compartments communicating
two-and-two by openings, as in Figure 12.
From the foregoing it will be seen that the improved commutator of
this Invention may be used either for establishing a permanent circuit or
an intermittent circuit which is automatically interrupted, or for sending
currents in different directions, by simply imparting a rocking motion to
a very light and simple apparatus in any suitable manner. Moreover
as the mercury box is hermetically closed, and the wires are protected
by an insulating covering, the apparatus may be used in any situation,
and the contacts and connections will be protected from derivations.

page_text: Many other applications might be made, all of which it would be too
long to enumerate, but they will be evident from the foregoing.
Having described the nature of the Invention, and the manner of
performing the same, I declare that what I claim as the Invention to be
protected by the herein-before in part recited Letters Patent is, a com-
mutator consisting of a vessel of non-conducting material capable of
being oscillated, divided into one or more compartments either separated
or communicating together (some only or all) by orifices, and containing
mercury, and having one or more electrical contacts so disposed that by
the tilting of the vessel in one or other direction the mercury varies in
position, and concurrently with the contacts cither closes or interrupts
the circuit or circuits for producing the electrical effect desired, all as
herein described, the said commutator being applicable, first, for reversing
electric currents either permanently, momentarily, or for a limited time,
according to the size of the orifices and the amount of mercury and the
position of the contacts; second, for establishing a current of limited dura-
tion, but only when the oscillation is in a particular direction and at a
certain speed, as in the case of hoists, for indicating the level of a liquid,
for giving warning of the passage of trains, for firing torpedoes, and
other purposes, as herein set forth; third, for controlling the working of
railway switches and signals; and, lastly, in other cases in which it is
desired to register the movements of machinery.
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In witness whereof, I, the said Alexander Melville Clark, have.
hereunto set my hand and seal, this Twenty-ninth day of April, in
the year of our Lord One thousand eight hundred and seventy-
five.