A Method of Ascertaining the Difference of Electric Potential at a Distant Extremity of Conductors.
Year: 1895

page_text: Date of Application, 1st Jan., 1895
Complete Specification Left, 31st July, 1895-Accepted, 31st Aug. 1895
I
PRUVISIONAL DIECIT RUATION.
A Method of Ascertaining the Difference of Electric Potential at a
Distant Extremity of Conductors.
JOHN HOPKINSON, F.R.S: Civil Engineer, of 5 Victoria Street, in the County
of. London, do hereby declare the nature of this invention to be as follows:-
My invention relates to means of ascertaining the difference of electric potential
at the extremity of conductors at a distance from the place of observation, as I shall
describe referring to the accompanying diagram.
:
A is an electric generator from which conductors' lead to lamps L. or other
consumers of electricity at a distance. In order to ascertain the difference of
potential at L, I connect the two conductors through resistances B K
= 1, and
DK. I connect the point K where these resistance conductors meet through
a cell C of known voltage, preferably a Clark cell, a switch S and a sensitive
galvanometer G to a point in the main conductor such that the resistance
of DH = r
r is to the resistance of the circuit DLB = R as the electromotive
force v of the cell C is to the desired potential difference V at the distant point L.
If, on observation, tlie galvanometer G is found to be not affected, then it is known
that is the difference of potential at L. This is proved as follows. Assuming
. I
the current = c, then the potential difference in HD is ✓ Rc, and, as the galvano-
meter is not affected the potential difference in KH is; the potential difference
v+Re = V + Rc, that is to say the desired difference of
in DB is
"
("
potential V plus Re the loss in the conductors.
i
The resistances may be adjusted by using different metals,, such as copper
and German silver, to suit variations resulting from changes of temperature or
other causes. Two cells may be introduced at C with suitable switches, so that
either can be used.
Also the cell or.
cells may be omitted, a voltmeter requiring little or no
current being interposed between the points K and H. If the voltmeter is suitable
for measuring alternating currents, this arrangement will measure the alternating
pressure at the farther end of the conductors.
1
H If the voltmeter requires a sensible current to actuate it, the resistance r has to
be suitably modified. For alternating currents, condensers may be used instead of
the resistances 1 T₁. The voltmeter introduced between the points and H may
be a quadrant electrometer or other electrometer of the same general character.
In this case the needle will be excited' by the difference of pressure between C and D
or Cand K and the quadrant by the difference of pressure between the points K
and H.
.:
:
In this case also it may be necessary to modify the resistance' DK as, according
to the conditions of the electrometer, the sensibility increases, is constant, or
diminishes with the difference of pressure between C'and D.
Dated this 1st day of January 1895.
...i

page_text: A Method of Ascertaining the Difference of Electric Potential at a
Distant Extremity of Conductors.
I, JOHN HOPKINSON, F.R.S. Civil Engineer, of 5 Victoria Street, in the County
of London, 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 means of ascertaining the difference of electric potential
at the extremity of conductors at a distance from the place of observation, as I shall
describe referring to the diagram accompanying my Provisional Specification.
=
A is an electric generator from which conductors lead to lamps L or other
consumers of electricity at a distance. In order to ascertain the difference of
potential at L, 1, connect the two conductors through resistances BK = 71, and
DK connect the point K, where these resistance conductors meet, through
a, cell C of known voltage, preferably a Clark cell, a switch S and a sensitive
galvanometer G to a point H in the main conductor such that the resistance
of D.H = is to the resistance R of the conductors to the distant point L as
the electromotive force of the cell C is to the desired potential difference V at
the distant point L. If, on observation, the galvanometer G is found to be not
affected, then it is known that V is the difference of potential at L. This is
proved as follows. Assuming the current = c, then the potential difference in H D
is. Rc, and, as the galvanometer is not affected, the potential difference in KH
is v; the potential difference in D B is "+" (" + " Rc) but as r, bas to (7) + rs)
1'
V
the ratio of a to V., the above expression becomes. ✗. (" + /Kc) = V + Re, that
17
is to say, the desired difference of potential V, plus Re the loss in the conductors.
The resistances r₁r, may be adjusted by using different metals, such as copper
and. Gernian, silver, to suit variations resulting from changes of temperature or
other causes. Two cells may be introduced at C with suitable switches, so that
either can be used.
Also the cell or cells, may be omitted, a voltmeter requiring little or no current
being interposed between the points K and H. If the voltmeter is suitable for
measuring alternating currents, this arrangement will measure the alternating
pressure at the farther end of the conductors.
If the voltmeter requires a sensible current to actuate it, the resistance r, has to
be suitably modified. For alternating currents, condensers may be used instead of
the resistances π₁
The voltmeter introduced between the points K and H may be a quadrant
electrometer or other clectrometer of the same general character. In this case the
needle will be excited by the difference of pressure between C and D or C'and K
aud the quadrant by the difference of pressure between the points K and H.
In this case also it may be necessary to modify the resistance DK as, according to
the conditions of the electrometer, the sensibility increases, is constant, or diminishes
with the difference of pressure between C and D.
Having now particularly described and ascertained the nature of this,inven-
tion and in what, manner the same is to be performed, I declare that what I
claim is:-
1. The herein described method of ascertaining the difference of electric potential

page_text: at a distant extremity of conductors by connecting near points of the conductora
through suitable resistances to each other and the meeting point of these connections
through a cell of known voltage and a galvanometer to another point on one of the
conductors selected so that the galvanometer is in balance when the difference of
potential at the distant extremity of the conductors is that for which the resistances
and cell are adjusted.
2. In combination with a pair of electrical conductors leading from a generator
to lamps or other consumers,, a cell of known voltage, a galvanometer and suitable
resistances connecting these to the leads, substantially as and for the purpose set
forth.
3. The modified arrangement wherein a voltmeter is substituted for the cell and
galvanometer, substantially as described.
Dated this 21st doy of Jul. 1805
ABEL & IMRAY,
Agents for the Applicant.