IMPROVEMENTS IN THE METHOD AEDAITIMA DY WRANG OR SWITCHG
Year: 1882

page_text: LETTERS PATENT to John Jamieson of Oldham in the County of Lancaster
Mechanical Engineer for an Invention of IMPROVEMENTS IN THE METHOD
AEDAITIMA DY WRANG OR
SWITCHG
PROVISIONAL SPECIFICATION left by the said John Jamieson at the Office
of the Commissioners of Patents on the 29th December 1882.
JOHN JAMIESON of Oldham in the County of Lancaster Mechanical Engineer
"IMPROVEMENTS IN THE METHOD OF CONTROLLING THE CURRENT IN ELECTRIC
CIRCUITS BY MEANS OF SWITCHES RESISTANCES AND SIMILAR APPARATUS
""
The object of my Invention is to vary or diminish the strength of current by
less expensive and more compact means than are at present generally employed
and to prevent or diminish the formation of a dangerous or destructive arc when
the current is broken by means of a switch or other arrangement.
To vary the strength of current I insert in the circuit special resistances con-
structed in the following or similar manner. I take a tube of nonconducting
material and fill it with thin discs of oxidised metal, at the ends of the tubes
I place discs of copper or other metal in contact with the external oxidised discs
and attach the two ends of the circuit wire thereto. The discs may be slightly
dished and be placed in pairs with their convex faces opposed and in any case an
arrangement may be provided for varying the amount of pressure between the
discs if desired. I prefer to use iron or steel for the discs well coated with the
black oxide. By this means a resistance of several thousand ohms may be made
to occupy a small fraction of the space required for a wire coil at a nominal cost.
For high resistances very small and thin discs may be used while for low resistances
or currents of great strength larger and thicker discs may be employed.
To prevent the formation of a dangerous or destructive arc on breaking the
circuit by means of a switch I employ two or more fixed contact plates or studs

page_text: arranged close to each other so that the movable contact shall touch the second
before leaving the first fixed contact between each pair of fixed contacts I interpose
one of the special resistances herein before described. When the Switch is moved
to break the circuit the resistances are successively added and therefore the strength
of the current is also successively diminished until all the resistances being included
only a small spark is formed if the circuit is broken. This spark may if desired be
obviated by leaving the movable contact of the Switch on the last fixed contact
in which case the circuit would not be completely broken and a current of
inappreciable strength would continue to flow in the circuit-Instead of using the
special resistances between the fixed contacts I may employ resistance coils, or
other usual form of resistance or any other special resistance such as carbon powder
metallic sulphides, oxides or salts which possess a low conductivity.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Jamieson in the Great Seal Patent Office on the 29th June
1883.
JOHN JAMIESON. of Oldham in the County of Lancaster Mechanical Engineer
"IMPROVEMENTS IN THE METHOD OF CONTROLLING THE CURRENT IN ELECTRIC
CIRCUITS BY MEANS OF SWITCHES, RESISTANCES AND SIMILAR APPARATUS
"
The object of my Invention is to vary or diminish the strength of the current
in Electric Circuits by less expensive and more compact means than are at present
generally employed and to prevent or diminish the formation of a dangerous or
destructive arc when the circuit is broken by means of a switch or other similar
arrangement or device.
To vary or diminish the strength of current I remove from or insert in the
circuit as the case may be special resistances constructed in the following or
similar manner. I take a tube of nonconducting material and fill it with thin
discs of oxidised metal and at the ends of the tube place electrodes or discs of
copper or other suitable metal in contact with the external oxidised discs and
attach the ends of the circuit wires thereto. Instead of a tube any equivalent
arrangement for holding the oxidised discs in position may be employed. The
discs may be flat or slightly dished. If they are dished it is best to place them in
pairs with their convex faces opposed. I prefer to use iron or steel for the discs,
well coated with black oxide as I find these give the best results. This black
oxide exists on sheet iron or steel as it leaves the rolling mill or it may be specially
formed or deposited on the iron or steel by well known methods. In some cases,
as for example when currents derived from a machine have to be dealt with I
interpose between the discs a further quantity of the metallic oxide in a powdered
form, or I dispense with the discs and insert the oxide alone between the electrodes
in which case I prefer to employ the black oxide of iron before mentioned which is
also known as " magnetic oxide of iron or where a higher resistance is required
I may employ the oxide of tin (Sn O 2). In any case an arrangement may be
employed for varying the amount of pressure between the electrodes as I find that
the resistance may be varied at will within very wide limits by modifications of
this pressure.
")
By means of resistances constructed in the manner herein before described a
resistance of several thousand ohms may be made to occupy a small fraction of the
space required for a wire coil and the cost will be very much less.
For high resistances and small strength or intensity of current small and thin
discs may be used. Thus for resistances to a current having a strength or
intensity of less than one ampere, the discs of iron or of steel may have a diameter
of one centimetre and a thickness of 0.3 millimetre each or less, and if the metallic
oxide alone is used the diameter of the tube or cell containing it between the
electrodes may also be about, one centimetre. The number of discs or the thickness
of the powered oxide must be governed by the required resistance, and can be
readily ascertained by the ordinary means of measurement.
For currents having a greater strength or intensity the discs (or the cell con-
taining the equivalent oxide) may have a larger diameter, but I prefer that the
diameter shall not exceed about 25 millimetres in any case and I prefer also with
such currents to use two or more resistances with their like electrodes connected
together, that is to say joined up in what is variously known as parallel circuit”
or "multiple arc," when the resistance is comparatively low relatively to the
strength of current for example less than 10 ohms with a current of 150 volt
amperes,
"

page_text: To prevent or diminish the formation of a dangerous or destructive arc on
breaking the circuit by means of a switch or otherwise I employ two or more
fixed "contacts" plates or studs arranged close together so that a movable contact
shall touch the second fixed contact before leaving the first.
This arrangement of a series of fixed contacts and a movable contact is well
known and is employed for the rheostat governing the strength of current in the
field magnets of the Edison and other shunt wound dynamo electric machines but
any equivalent device may be used. Between each pair of fixed contacts I
interpose a special resistance constructed as herein before described. When the
movable contact of the switch is moved to diminish the current or break the
circuit the resistances are successively added to the circuit and therefore the
strength or intensity of the current is gradually diminished until all the resistances
being added only a small spark or arc is formed if the circuit is then broken..
This minute spark or are may be obviated by leaving the movable contact of the
switch on the last fixed contact in which case the circuit would not be completely
broken and a current of inappreciable strength or intensity would continue to flow
in the circuit. It will be understood that the reverse motion of the movable
switch will gradually restore the current to its initial strength. An equivalent
arrangement may also be employed when it is merely desired to insert the
resistances in circuit and remove them therefrom at will.
Having thus described the nature of my Improvements and the best means
known to me of carrying them into practical effect I desire it to be understood
that I do not limit myself to the precise details herein given as the same may be
varied without departing from my Invention but that what I claim is.
First. The resistances constructed substantially as and for the purposes
herein before described.
Second. The method of controlling the current in electric circuits by the com-
bination of the resistances constructed substantially as hereinbefore described with
an arrangement for placing the resistances in circuit or removing them therefrom
for the purpose of varying the strength or intensity of current.
Third. The method of controlling the current in electric circuits by the com-
bination of the Resistances constructed substantially as herein before described with
a switch or circuit breaker for the purpose of diminishing or preventing the
formation of an arc.
In witness whereof I the said John Jamieson have hereunto set my hand
and seal this twenty-fifth day of June in the year of our Lord one
thousand eight hundred and eighty three.