Improvements in Electrical Resistance Devices.
Year: 1896

page_text: Date of Application, 3rd Nov., 1896-Accepted, 6th Mar., 1897
COMPLETE SPECIFICATION.
Improvements in Electrical Resistance Devices.
.
I, GEORGE KING CUMMINGS, of Monadnock Block corner of Dearborn and
Jackson Streets, Chicago, in the County of Cook and State of Illinois, United
States of America, Electrical Expert, 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 certain new and useful improvements in electrical
résistance devices, which may be employed for regulating an electric current
by offering more or less resistance to its passage, or used as an electric heating
device.
The object of the invention is to provide a resistance device composed of a
number of resistance members, the total resistance of which can be varied by slight
gradations; and a further object is to provide a simple and inexpensive construction
and arrangement of parts which can be readily manipulated to accomplish the
results sought for.
With these and other ends in view, the invention contemplates a number of
resistance members, one form of which is filled with a suitable resistance material,
and two terminals arranged in the resistance material of each member, one of which
terminals is adapted to be adjusted in the material, whereby the total resistance
may be permanently varied by connecting said members in series, in multiple, in
multiple series or in series multiple, and yet the total resistance may also be readily
varied irrespective of the method of connecting the members.
The term "member," as used by me in this specification, is to be understood as
indicating a portion of a total resistance that has attached thereto two electric
connections, through which such portion or member may have electrical connection
with the circuit..
The invention consists also of certain other features of construction and details
which will be fully hereinafter described.
In the accompanying drawings forming a part of this application--
Figure 1 is a front view of the device.
Figure 2 is a side elevation.
Figure 3 is a view, partly in section, with the front plate removed.
Figure 4 is a sectional view, on the line 4-4 of Figure 3.
Figure 5 is a sectional view on the line 5-5 of Figure 3 ; and
Figure 6 is a detail view of a modified form of a member.
Like letters of reference. denote corresponding parts in all the figures of the
drawings.
A designates the front plate, which is secured to the frame B by means of the
screw-rods 6 at the corners of said frame. Two or more transverse rods C are
secured to opposite sides of said frame, and movable cross-pieces D, E are mounted
on said rods. A rack-bar F is secured at its ends to the cross-pieces and is
arranged to mesh with a toothed-wheel f, which is mounted on a suitable shaft. ft
and is operated by means of the wheel G.
In the drawings, I have illustrated the resistance members in the form of tubes
or cylinders J, which is a convenient construction, but my invention is not limited
to any particular form or construction of the 'members, for it is obvious that many
other forms may be employed. For example, I may employ a rod of some

page_text: resistance material and a box containing mercury adapted to be adjusted on said
rod, one wire being connected to the box and the other to the rod in some suitable
manner; or, instead of the box containing mercury, I may use a brush. The
members may be embodied in many other forms which it is unnecessary for me to
mention here. The tubes J are mounted between the cross-pieces D, E, and the
ends of the tubes are fitted in recesses g in the faces of the cross-pieces, being
preferably provided with a screw-thread for this purpose. I may employ any
number of these tubes more than one, and it is not at all essential that they should
be of any particular form or configuration, the only requirement being that they
shall contain a sufficient quantity of resistance material for the purposes of the
invention. The tubes are filled with suitable resistance material J1, and I have
found that powdered graphite, from 50% to 90% pure, is the preferred material,
as it accomplishes the results of my invention in a superior manner. I would have
it understood, however, that I do not hereby limit myself to any particular
resistance material.
Each of the members and the parts connected therewith are substantially alike,
and I will therefore only describe one of them. A rod H, which forms one of the
terminals, extends into one end of the tube and it is secured at its other end to a
stationary cross-piece I at one side of the frame.
It will thus be observed that, as the wheel G is operated, the toothed-wheel f
meshing with the rack F, moves the two cross-pieces D, E on the rods C, and the
tube is adjusted farther on or off of the long terminal-rod H. Referring
particularly to Figure 3 of the drawing, if the toothed-wheel is turned to the left,
the short rod will be moved farther away from the long rod H, and the resistance
afforded by the material between the terminals is thereby increased; and, if the
wheel is turned to the right, the rod his brought closer to the rod H and the
resistance decreased.
'Although I have shown and described the tubes as arranged and adapted to be
adjusted on the rods H, it is obvious that the cross-pieces, D, E may be made
stationary and the cross-piece I movable, so that the rods H can be adjusted in
the tubes."
As hereinbefore stated, the tubes J may be of any form or shape adapted to the
particular purposes for which they are intended, and they may be cast or fashioned
with irregular exteriors to increase the heat radiating surfaces. They are preferably
made of metal and lined or coated with enamel, or other insulating substance. The
electric current is carried to the terminals in a suitable manner, and it is regulated
by the resistance offered by the amount of granulated or powdered material
between the adjacent ends of the rods h H, the density of said material being
substantially constant. The shorter rod does not move into. the tube, but, when.
the cross-pieces D, E are operated, the tube is moved onto the long rod H, and
the resistance of the material between the contact-rods is increased or decreased in
exact ratio to the length of the movement of the tube.
It is essential that there should be sufficient resistance material in the tube so
that a sufficient "carrying capacity" may at all times be provided between the ends
of the terminals, whether they be close together or far apart.
'The contact-rods may be connected in series, in multiple, in multiple series or in.
series multiple, as desired, and in any combination where a number of members
are employed each member thus bears an equal share of the total energy consumed
in resistance.
The wheel or handle G, which may be of any desired construction, is preferably
constructed so that one turn or revolution thereof will move the tube throughout
its entire limit of movement, but this, of course, may be varied as desired.
I have shown in the drawings a number of tubes, all of which are constructed
alike, and any number of them may be employed. In order that the device may
not be too bulky in size, I prefer to proportion the parts for a comparatively high
temperature of the members, and to use a resistance material not only of a high
resistance, but one which will not easily fuse and which is capable of remaining

page_text: unchanged in its chemical and structural formation upon the application of very
high temperatures.
As the actual radiating surfaces of the tubes are protected by the frame, it is
evident that they may be safely heated to a very high temperature without danger
of fire, the exterior of the device being heated only by conduction by the air
currents passing through the openings in the sides K of the frame. By the use of
my improved construction, I entirely avoid the sparking and arcing at the contact
points, which usually occur in devices of this character, as well as the liability of
forming rough and uneven electrical terminals which tend to decrease the brilliancy
of the light supplied by the current; and the gradations are so uniform and small,
and the decrease of brilliancy so gradual, that the eye cannot detect any jump or
unevenness of light when the resistance is increased or decreased, but merely an
even gradation.
It will be observed that in decreasing the total resistance of the device, it is
unnecessary to cut out any member, whereby the practical heat radiating surface
of the device is increased and that portion of the member which is not active
electrically is in the best possible juxtaposition to the active portion for the purpose
of aiding in dissipating the heat from the active portion.
In Figure 6, I have illustrated another of the many forms of members which
may be employed in connection with my invention, which contemplates the
employment of a liquid or semi-liquid resistance material J, in which the
terminal H is adapted to be adjusted after the manner of a plunger. The
construction of parts and operation of this device are substantially similar in
every way to that hereinbefore described, and I will not enter into a detailed
description thereof.
Where large currents are required to be passed through the device, I find
it desirable to connect the members in multiple or multiple series, in which.cases
the passage of the current does not depend upon any one contact, but it divides its
path proportionally to any defects that may occur in the electro-mechanical
construction of the device.
By using a number of resistance members, I am able to provide a device in
which all of said members may be adjusted to provide a total gradation of
resistance, and I am, therefore, also able to construct my device in a convenient.
and advantageous manner so that it will not be likely to burn out. If desired, one
or more of the members may be entirely cut out of the circuit.
I am aware that changes in the form and proportion of parts and details of
construction of the invention may be made without departing from the spirit or
sacrificing the advantages thereof, and I, therefore, reserve the right to make all
such changes as fairly fall within the scope and spirit of the invention.
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 :-
1. An electrical resistauce device comprising a number of members whose density
is constant, the resistance of one or more of which members is capable of being-
mechanically varied, substantially as described.
2. An electrical resistance device comprising a number of members, the resistance.
of all of said members being capable of simultaneous variation, substantially as
described.
3. In an electrical resistance device, the combination with a number of resistance
members comprising the resistance of the device, of means for varying the resistance.
of said members simultaneously, substantially as described.
4. In an electrical resistance device, the combination of a number of separate
and independent resistance members, and means for collectively controlling the
resistance of said members to vary the total resistance, substantially as described.
5. In an electrical resistance device, a number of resistance members connected
in series, in multiple, in multiple series or in series multiple, and means for-

page_text: increasing or decreasing the combined resistance of said members by the adjustment
of the resistance between the terminals of each resistance member, substantially as
described.
6. The combination with a number of tubes filled with electric resistance
material, of a terminal-rod rigidly secured in one end of each of said tubes, and
another terminal-rod arranged in the other end of each of said tubes, substantially
as and for the purpose set forth.
7. The combination with a number of tubes containing electric resistance
material, of a terminal-rod arranged in each end of each of said tubes, and means
for adjusting the tubes on some of said terminal-rods to increase or decrease
the resistance between the ends of said terminal-rods, substantially as described.
8. The combination of a. frame, the cross-pieces movably secured in said frame,
a number of tubes. arranged between said cross-pieces and containing suitable
resistance material, a terminal-rod secured in one end of each tube, and another
terminal-rod arranged in the other end of each tube, and means for moving said
cross-pieces to adjust the tubes on some of said terminal-rods, substantially as
described.
9. The combination of a frame, the cross-pieces movably secured in said frame,
a number of tubes arranged between said cross-pieces and containing suitable
resistance material, a terminal rod secured in one end of each tube, another
terminal-rod arranged in the other end of each tube, a rack-bar secured between
said cross-pieces, and a toothed-wheel arranged in engagement with said rack-bar
and adapted to be operated to move the cross-pieces, substantially as described.
10. The combination of a frame, the rods secured in said frame, the movable
cross-pieces mounted on said rods, a number of tubes secured between said cross-
pieces and containing an electric resistance material, a terminal-rod rigidly secured
in one end of each tube, a stationary cross-piece, a terminal-rod arranged in the
other end of each tube and secured to the stationary cross-piece, a rack-bar
connecting the movable cross-pieces, a toothed wheel arranged in engagement with
said rack-bar, and a handle for operating said ratchet-wheel whereby the tubes
may be adjusted to increase or decrease the resistance between the ends of the
terminals, substantially as described.
11. An electric resistance device composed of a number of semi-solid resistance
members whose density is constant.
Dated this 3rd day of November 1896.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.