IMPROVEMENTS IN DIPPERENTIAL GALVANOMETERS."
Year: 1868

page_text: LETTERS PATENT to Josiah Latimer Clark, of Beechmont, Sydenham
Hill, in the County of Surrey, for the Invention of "IMPROVEMENTS
IN DIPPERENTIAL GALVANOMETERS."
"
Sealed the 5th September 1868, and dated the 5th March 1868.
PROVISIONAL SPECIFICATION left by the said Josiah Latimer Clark
at the Office of the Commissioners of Patents, with his Petition,
on the 5th March 1868.
I, JOSIAH LATIMER CLARK, of Beechmont, Sydenham Hill, in the
County of Surrey, do hereby declare the nature of the said Invention.
for "IMPROVEMENTS IN DIFFERENTIAL GALVANOMETERS," to be as follows:-
This Invention has for its object improvements in differential
galvanometers, and consists in the construction of an improved form
of testing galvanometer by a new arrangement of the circuits of a
differential galvanometer so as to make it more portable and equally
applicable for measuring delicate currents and for testing the insulation
of telegraph lines, and also for measuring powerful currents, and for
ascertaining the internal resistance of batteries.

page_text: The improvement is effected by attaching a shunt or derived circuit
to both of the coils of a differential galvanometer as a permanent part
of the machine, and by providing plugs by which either or both of the said
derived circuits or shunts can be thrown into operation; and I combine
this improvement with a certain arrangement or disposition of the
terminals and connections and a peculiar key, which, though not in
itself new, renders the whole combination superior to any form of
testing galvanometer hitherto known.
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Josiah Latimer Clark in the Great Seal Patent
Office, on the 5th September 1868.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOSIAH
LATIMER CLARK, of Beechmont, Sydenham Hill, in the County of
Surrey, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria by Her
Letters Patent, hearing date the Fifth day of March, in the year of
our Lord One thousand eight hundred and sixty-eight, in the thirty-first
year of Her reign, did for Herself, Her heirs and successors, give and
grant unto me, the said Josiah Latimer Clark, Her special licence that
I, the said Josiah Latimer Clark, my executors, administrators, and
assigns, or such others as I, the said Josiah Latimer 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, exercise, and
vend, within the United Kingdom of Great Britain and Ireland, the
Channel Islands, and Isle of Man, an Invention for "IMPROVEMENTS IN
DIFFERENTIAL GALVANOMETERS," upon the condition (amongst others) that
I, the said Josiah Latimer 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.

page_text: NOW KNOW YE, that I, the said Josiah Latimer 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, that is to say :-
This Invention has for its object improvements in differential
galvanometers, and consists in the construction of an improved form
of testing galvanometers by a new arrangement of the circuits of a
differential galvanometer so as to make it more portable and equally
applicable for measuring delicate currents and for testing the insulation
of telegraph lines, and also for measuring powerful currents, and for
ascertaining the internal resistance of batteries.
The improvement is effected by attaching a shunt or derived circuit
to both of the coils of a differential galvanometer as a permanent part of
the machine, and by providing plugs by which either or both of the
said derived circuits or shunts can be thrown into operation, and I
combine this improvement with a certain arrangement or disposition of
the terminals and connections and a peculiar key which, though not in
itself new, renders the whole combination superior to any form of
testing galvanometer hitherto known.
The way in which I prefer to carry out this Invention in practice is
shown in the diagram, Figure 1.
This instrument is a form of differential galvanometer, that is to say,
it is wound with two separate wires which form distinct circuits around
the needle, one circuit extending from A to B, and the other from C to D.
These wires are both adjusted to have the same electrical resistance and
also to have the same effect on the needle, so that when a battery is
connected to the two central terminals B and C the current divides
itself into two equal portions, one flowing from B to A and tending to
deflect the needle to the left, the other from C to D deflecting it to
the right, but since the quantities and forces are precisely equal the
needle remains quiescent. If equal resistances be added on each side
of the galvanometer the needle still remains motionless, but if unequal
resistances be added more electricity flows to that side which has the
lesser resistance, and the needle is deflected to that side. The peculiarity
of the instrument consists in the addition of a "shunt" or derived
circuit to each half of the galvanometer; these shunts are marked on the
instrument "shunt roo"; they are short wires having a resistance equal
to exactly th of that of the half coil (or such other proportion as may

page_text: be preferred), and when thrown into circuit by the insertion of the
plugths of the current pass through them, and only roo through
the coils of the galvanometer, either one or both half coils may be
shunted at pleasure. The instrument is supplied with a set of resistance
coils varying from one to ten thousand ohms. When it is desired to
make the instrument very small and portable I prefer to employ a flat
coil wound horizontally, as in Figure 2, and within the centre of the
coil I suspend on a fibre a small magnet, straight or curved, which
is balanced in a horizontal position on a silk fibre, and which carries a
vertical bristle or stem as a pointer; or instead of a pointer I sometimes
cause it to carry a light horizontal mirror, the motions of which, when
looked down upon from above, are very easily observed, but I do not
claim either of these forms as a part of my Invention. A directing
magnet may be used for adjustment.
In this Invention I claim as original the method of employing definite
shunts or derived circuits to both the coils of a differential galvanometer
in order to render it equally applicable for the various measurements
which occur in practical telegraphy.
In witness whereof, I, the said Josiah Latimer Clark, have hereunto
set my hand and seal, this Twenty-first day of August, in the
year of our Lord One thousand eight hundred and sixty-eight.
JOSIAH LATIMER CLARK. (L.S.)