Improvement in Exchange or Central Office Systems as Applied to Telegraphs, Especially Autographic Telegraphs.
Year: 1889

page_text: Date of Application, 14th May, 1889-Accepted, 19th Apr., 1890
COMPLETE SPECIFICATION.
Improvement in Exchange or Central Office Systems as Applied to
Telegraphs, Especially Autographic Telegraphs.
I, HERBERT JOHN ALLISON, of 52 Chancery Lane, London, in the County of
Middlesex, Patent Agent, do hereby declare the nature of this invention, (which has
been communicated to me from abroad by James Hart Robertson, Electrician, residing
at the corner of Sylvan Street and The Terrace, Rutherford, Bergen County, New
Jersey, United States of America), and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement :-
This invention is intended to be used in connection with the autographic telegraphs
for which United States Letters Patent have been granted to James Hart Robertson,
viz., No. 350320, dated October 5th 1886; No. 353592, dated November 30th 1886;
No. 353593, dated November 30th 1886; and No. 353594, dated November 30th
1886, notably No. 353593 dated November 30th 1886.
The instruments of such a telegraph are, of course, adjusted to operate at a certain
resistance of the circuit, i.e. they are so adjusted that they will operate best at a
particular resistance. When, however, numerous instruments, located at various
points, are connected with a Central Office, it follows that there will be a great
difference in the resistance of the several connecting conductors, and that in those
cases where the resistance of the circuit differs widely from that to which the instru-
ments are adjusted, the latter will not work satisfactorily, or perhaps not at all. To
adjust in each such case, the resistance of the instruments would be impracticable as
it would require experienced operators, the employment of which it is desired to
make unnecessary.
It is therefore desirable to have some means whereby the com-
bined resistance of any two subscriber's lines that may be connected with each other
may be made approximately the same. I accomplish this object by the means herein-
after described and claimed.
In my patent herein before referred to, I have shown and described the instruments
of subscribers connected and operated by two conductors, but for the sake of clearness,
I have shown in the accompanying drawing only one conductor. It is, however,
possible to operate the instruments by only one connecting conductor as described in
Cowper's English Patent No. 1242 of 1879 for example.
In the drawing herewith forming part of this specification is shown a construction
embodying my invention, for accomplishing the object I have in view.
In the drawing I have shown six subscribers lines, 1, 2, 3, 4, 5, 6, of varying
resistance entering a central office. Two switches 7, 8, electrically connected with
each other are used for connecting the several subscribers with each other. In the
conductor connecting the switches is placed the battery 9. I have shown two lines
of 200 and 100 ohms resistance connected with each other, making a combined
resistance of 300 ohms, disregarding resistance of battery. If lines and 5, were
connected with each other, the combined resistance would be only 22 ohms. As all
the instruments of the several subscribers are adjusted approximately the same, it is
obvious that the battery suitable for a circuit of 300 ohms resistance would be too
strong for a circuit of only 22 ohms resistance. To remedy this difficulty, I provide
each line with an equalizing resistance, which, as shown in the drawing consists of a
pile of carbon disks 10. This resistance is adjusted for each line, and is inserted in
the same at the Central Office. No two subscribers lines out of a thousand are likely
to be of the same resistance, and hence I add to each line after it has entered the
Central Office sufficient resistance to make all the lines equal in that respect. I prefer
to use piles of carbon disks, each pile provided with an adjusting screw 11, whereby
the resistance can be increased or decreased as may be found necessary.

page_text: 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. In autographic telegraphy the combination with a number of conductors of
different resistances extending from the subscribers instruments to and terminating in
a central office, of switching means for electrically connecting any two of said con-
ductors, and equalizing resistances, whereby the combined resistance of any two con-
ductors that may be connected with each other is made approximately the same,
substantially as described.
2. The combination with a number of conductors of different resistances, terminating
in a Central or Exchange Office, of a pile of carbon disks inserted in each conductor,
each pile being provided with an adjusting screw for adjusting the resistance thereof,
whereby the combined resistance of any two conductors that may be connected with
each other is made approximately the same, substantially as described.
Dated this 14th day of May 1889
ALLISON BROS.,
Agents for the Applicant.