Electrometers.
Year: 1891

page_text: Date of Application, 26th June, 1891
Complete Specification Left, 26th Mar., 1892-Accepted, 21st May, 1892
Electrometers.
I CHARLES VERNON BOYS F.R.S. of 11 Alexander Square S.W. in the
County of Middlesex Professor of Physics do hereby declare the nature of this
invention to be as follows
My invention relates to modifications of the quadrant electrometer invented by
Sir William Thomson.
I make the needle out of an even number of sectors which nearly complete the
form preferably of a disc or a cylinder. Alternate arms are kept oppositely
electrified by contact with the ends of a dry pile forming part of the needle, or by
connecting one set to one terminal of a Leyden jar or a battery or other charged
body and the other set to the other terminal of the jar, battery or other charged
body as the case may be. The two sets of arms may be conveniently connected
to the above, one by a torsion wire, spring or metallically coated fibre and the
other by a similar connection or by wire dipping in a conducting fluid in the usual
way.
I sometimes keep the alternate sets oppositely electrified by making them or
coating them with different substances so as to make use of their contact difference
of potential. The needle may then conveniently be made in the form of a complete
disc or cylinder.
I make the part usually called the quadrants, but which I shall call the sectors,
in the usual way except that there must be one sector for each arm of the needle,
but when it is important that they should have small capacity I make them of
a narrow form so as to correspond in this respect to the width of needle used in
electrometers as ordinarily constructed.
If the instrument is required for measuring alternating differences of potential I
make the needle with thin or narrow arms corresponding to each division of the
sectors. If made of one metal and placed unsymmetrically, it tends to move round
towards a symmetrical position with each arm opposite to a sector whichever
way the electro motive force is applied. If made of two pieces differently electrified
it will for feeble steady forces move in a direction depending on the direction of
the electro motive force, while with alternating electro motive forces it will act
as if made of one piece only.
Or I make the needle of a number of arms insulated from each other, in which
case if unsymmetrically placed it will tend to move into a symmetrical position
with each arm opposite to a division between two sectors, whichever way the
electro motive force is applied and so respond to alternating electro motive force.
Any of these forms are suitable for ballistic purposes.
In those cases where I make use of contact difference of potential to charge the
needle I obtain delicacy by making the instrument very small and using for the
torsion fibre a filament made of glass or preferably of quartz.
Dated this 26th day of June 1891

page_text: COMPLETE SPECIFICATION.
Electrometers.
I CHARLES VERNON BOYS F.R.S. late of 11 Alexander Square but now of
No. 7 Brompton Square both S.W. in the County of Middlesex Professor of
Physics 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 improvements in the quadrant electrometers invented by
Sir William Thomson. I make the needle out of an even number of sectors which
nearly or quite complete the form preferably of a disc or of a hollow cylinder.
Alternate sectors are kept oppositely electrified or at different potentials by
contact with the ends of a dry pile forming part of the needle.
For this purpose
I use a very small insulating tube (1) forming the axis of the needle which I fill
with minute discs such as are used in a dry pile but very much smaller. I connect
onc set of alternate sectors (+) to one end of the pile and the other
set () to the other end, the two sets together nearly completing a cylindrical
form, the gaps being only so much as is necessary for insulation of one set from
the other. suspend the needle preferably by a quartz fibre, or sometimes I
mount it on pivots, within cylindrical sectors corresponding in number with the
sectors in the needle and taking the place of the quadrants in the ordinary
electrometer. prefer to insulate them by supporting them by rods of fused
quartz. I sometinics make the fixed sectors by silvering or metallically coating
the inside of a glass tube (T) and separating with a cutting point the continuous
film into as many divisions (1) as may be required.
I sometimes keep the alternate sectors of the needle at different potentials
by connecting them with the terminals of an electro static or of a voltaic
battery of suitable power for which purpose the supporting fibre may be made
of or coated with metal to serve as one conductor while a second wire or con-
ducting fibre serves as the other conductor either dipping in acid as is usual or
connected rigidly to a fixed part of the instrument as may be most convenient.
sometimes avoid the use of dry piles, batteries &c. and still keep a sufficient
charge or difference of potential on the alternate sectors by making them of or
coating them with, different materials which by their contact produce the desired
result. Thus a disc composed of alternate quadrants (or sextants, octants &c.)
of platinum and zine (Fig. 2) I find to answer well or in the place of platinum
a coating of peroxide of lead or manganese or of similar material may be
used. In these cases I prefer to make the needle in the form of a complete
disc or cylinder but prefer the disc form.
For the purpose of measuring alternate differences of potential I make the
needle in the form of a star composed of a number of arms corresponding in
number and form with the fixed sectors and I so suspend the needle that when no
electro motive force is applied to the fixed sectors the arms of the needle shall
rest unsymmetrically, for instance each should lie about three quarters within one
sector and the other quarter within the other sector Fig. 3. The needle is then
deflected by induced action towards a symmetrical position when alternate (or even
when steady) electro motive forces are applied to the fixed sectors. The alternate
electro motive force may therefore be measured by the deflection of the needle
or by the torsion that must be applied in order to bring it back to its initial
position.
I sometimes combine the two instruments in one by making the last described
star shaped needle with alternate arms of different materials in which case it
acts as a sensitive instrument for steady electro motive forces while for alternating
electro-motive forces it acts as if the needle were of one material only.

page_text: I sometimes make the needle of a series of arms alternate sets being insulated
from each other.
I
I prefer to make needle and sectors much smaller than usual especially when
I use contact electricity to keep the two parts of the needle differently electrified.
For instance I have found that a needle made of a disc of foil one centimetre in
diameter and as thin as possible, alternate quadrants being of zinc and platinum
will when delicately suspended by a fine quartz fibre show a considerable degree of
delicacy and be independent of all charging batteries jars or cells.
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 an electrometer the use of a needle made of alternate sectors kept at
different potentials or differently charged.
2. The here-in-before described methods of keeping the alternate sectors of the
needle at different potentials or differently charged namely by the use of a dry pile
forming part of the needle, or by the use of conducting fibres or wires connecting
the two parts of the needle with an external charged body or by using contact
electricity simply.
3. The use of an unsymmetrically placed needle and sectors as described for
measuring alternate differences of potential.
4. The combination needle by which either feeble steady or alternating difference
of potential may be measured.
Dated this 26th day of March 1892
C. V. BOYS.