Improvements in Electrometers and in Keys for Operating the sam
Year: 1898

page_text: Date of Application, 6th Dec., 1898
Complete Specification Lett. 6th Sept. 1899-Accented 4th Nov 1899
PROVISIONAL SPECIFICATION.
Improvements in Electrometers and in Keys for Operating the sam
I, GEORGE LEONARD ADDENBROOKE, Consulting Engineer, of 53, Victoria Street,
Westminster, London, S.W., do hereby declare the nature of this invention
to be as follows:-
-
It is to render electrometers more sensitive, accurate, portable, more easily
adjusted, to increase their range, to fit them for use as volt & wattmeters &
ammeters particularly for alternating currents & to make them engineering
instead of distinctly laboratory instruments.
To effect this I suspend the needle from a metal strip or wire, the needle
itself being specially light. provide means of raising & lowering the needle,
& the quadrants are also adjustable as regards their upper & lower faces which
can be set at varying distances apart. The quadrants & needle are supported
in a special manner to secure high insulation & easy access & a number of
means of adjustment are employed which can only be described in detail.
The key has its contacts carried on pillars which are specially insulated
& the levers and the working of them are different to the means usually employed
but can only be described in detail.
The objects of my invention relate to electrometers and are;—
1. To render the instruments more sensitive.
2. To render the instruments more accurate.
3. More portable.
4. To render the instruments more easily adjusted and used.
5. To increase their range.
6. To enable them to be more easily used as voltmeters, and watt meters
or with a resistance as ammeters in addition to their other uses.
7. To permit their use for all forms of alternating measurements at high
or low potentials.
8. To reduce their cost
9. To fit them for use in engineering works, and central stations instead
of being only laboratory instruments.
10. To provide a key to facilitate the working of such instruments.
To obtain these objects I proceed as follows:
-
Taking the Kelvin type of quadrant electrometer as an example, as being
well known:-
In the first place the suspension does not usually consist of a silk or other
insulating fibre, though for particular purposes I may employ a single fibre
with a small directing magnet but preferably of a strip of very fine wire,
rolled flat, of some hard and spring metal, and the strip should preferably be
lightly gilded to prevent it from possible action of the atmosphere. I do not
limit myself to any particular breath thickness or length of strip, in fact I
use them of varying dimensions, according to the exact purpose for which the
electrometer is needed. At the same time I may say that a length of 7 to 10

page_text: inches in conjunction with the needle and other arrangements I am about to
describe is sufficient to attain a high degree of sensitiveness without too long
a period of oscillation. A similar metallic wire may be used instead of the
strip, or even in some cases a carbon filament such as is employed in lamps,
or a quartz fibre plated with some metal.
The use of a conducting strip or wire of this character metallically con-
nected to the needle and hanging from a highly insulated support, enables
the needle to be charged directly and without the use of a wire dipping into
sulphuric acid, as is commonly the case." This has the advantage of enabling
the needle to be fully charged when the electrometer is used idiostatically or
otherwise for measuring alternating currents even of a very high frequency
nor is there likely to be any error introduced as in the case with sulphuric
acid, if an alternating current of high frequency but low voltage has to flow
through it in order to reach the needle. It is also known that in sensitive
instruments the sensibility is considerably diminished if a wire from the moving
part depends into a liquid, owing to the surface tension.
If the electrometer is to be used heterostatically I do not employ a charged
jar as a rule to raise the needle to a high potential, or at any rate such a
charged jar does not form part of this instrument, such a method may be used
for certain purposes, the jar being separate from the instrument, but for most
purposes I employ a battery of small cells in series, and this is the easier. to
do as the instrument, is so sensitive that an ample deflection can be obtained
with a difference of potential of one volt between the quadrants when the
needle is charged, with about 30 or 40 volts.
Although the use of the needle in this way has great advantages it also
introduces a great difficulty, the overcoming of which I consider one of the
points of my invention. The difficulty is that although very definite and con-
stant the controlling force of a fine strip as I have alluded to is very slight,
and it requires special care and contrivance to prevent the needle from oscil-
lating for a very long period before it comes to rest which would make the use
of the instrument tedious. It is true that light vanes of mica or other material
may be employed, but I find if they are used they get charged after a time
and produce deflections themselves, on the other hand if metal is used it adds
to the weight and also causes attractions which often do more harm than good,
though under certain circumstances I do employ metal vanes to bring the
needle to rest sooner. I have found however by careful experiments that if
every precaution is taken to make the needle as light as possible its momentum
will be so reduced that it will come to rest in a reasonable time without any
other damping device while the lightness of the needle also improves the
sensitiveness.
To make a needle to fulfil these requirements I take a sheet of the thinnest
aluminium which may be of any shape suitable for the purpose, corrugated or
not and with holes perforated through it or otherwise. I do not confine myself
to the usual canoe shape though on the whole so far I have found this as con-
venient as any other. This needle has a light aluminium wire axis attached
to it by rivetting up one end of the wire so as to make one end of it like the
head of a pin, a small aluminium washer is then threaded on this, then the
needle is threaded on, then another washer. By means of a hollow punch the
whole are then forced together into metallic contact by a few blows, and a firm
joint is made. Another way of making the junction is to electroplate a portion
of the aluminium needle and the wire axle with copper, gold, or silver, and-
solder the two together with a solder of low fusibility. A portion of the round
wire axle is filed flat to take the mirror, & the needle can be attached to this
strip in any of the following ways.
1. The end of the wire axis may be plated with copper to which the strip can
then be easily soldered.
2. The end of the wire may be split and the end of the strip be placed in the
:

page_text: cleft, and the two sides be then firmly pressed together, thus holding the strip
between them.
3. The end of the wire axis may be flattened out and annealed, and bent
somewhat first to one side then to the other, the end of the flattened wire is
then bent over SO as to form a flat hook, the loop of which is
nearly at right angles to the axis of the needle itself. The strip is
then inserted in the flat hook, and the hook pressed flat with a pair of pliers
thus firmly clamping the strip; of the three methods the first has advantages
but I give the other two as practical methods which obviate any possible
chance of softening or altering the strip by heat. The other end of the strip
is either directly clamped in a little fork worked by a thumb screw, or the strip
may be attached by soldering, or otherwise to a small metal cylinder, or plate,
which can then be clamped in the fork or other means of suspension, this latter
method is convenient, when needles with strips of varying strength require to
be frequently used.
0
After the needle is thus built up and arranged I fix it in a clamp with the
axis horizontal and the blades of the needle vertical and at convenient height.
I then bring up from below a jar containing caustic soda or potash, or weak
hydrochloric acid into which the needle is caused to dip, to any depth desired
this solution I keep in motion, by which means the needle may be evenly eaten
away to any desired amount and by drawing the solution gradually
away this can be made to take place to the greatest extent at the broad por-
tions, and the outer edges of the needle which contribute most to the momentum
when the needle is suspended; if desired narrow lines of wax or varnish can
be drawn on the needle before this is done, so as to leave stronger ribs. By
treatment in this way I can make a needle of the usual size to weigh 3 grains.
The only addition to this is the weight of the mirror, such a needle suspended
by about 7 inches of No. 0 phosphor bronze wire rolled into a strip, the needle
being placed between quadrants the upper and lower inner faces of which are
about one fifth of an inch apart, and the needle between them, so that the needle
is about one tenth inch from the upper and lower faces of the quadrant, will
when coupled up, ideostatically give a deflection of about three millimeters,
when the electrometer is used as a reflecting instrument and the scale is situated
at 2 meters distance. Greater sensitiveness may be obtained by having 2 or
more needles on the same axis, mounted and treated as above, or
needles of other known forms such as a cylinder may be used or I some-
times make a needle of a long flat strip, the two ends of which are bent ver-
tically downwards. One or more of these strips of different radii may be used
and they are arranged to work between quadrants consisting of segments of
concentric cylinders standing up vertically.
Having described the needle I now proceed to describe the particular form
of quadrants, which I prefer and the general arrangement of the rest of the
instrument in order to secure the advantages enumerated above.
I proceed somewhat differently accordingly, as the instrument may need to
maintain a charge on the needle or quadrants for a long time, or if it is intended
for use primarily with alternating currents, when the insulation though requir-
ing to be good does not need to attain the same perfection. To avoid prolixity
I shall however describe an instrument of the first class. If any instrument
of the second class and somewhat more portable is required, some of the pre-
cautions described may not be needed or may not be required to be carried
so far.
Frequent experiments have shown me that it is of great importance that the
needle and its suspension complete should be able to be taken out or put in
the instrument without its being liable to be bent, or deformed in any way,
and also that this should be able to be done quickly. This I have found very
difficult to do with instruments of the Kelvin type or of Mascarts modification
although the form there used may be the best when sulphuric acid has been

page_text: used, both for making contact with the needle and for keeping the interior dry.
In my case I do not need to make the contact with the needle through liquid,
and have succeeded in gaining sufficient insulation without drying the interior
with sulphuric acid.
If practically perfect insulation is required for some special case, sulphuric
acid phosphoric acid and other absolvent can be introduced easily in a recep-
tacle of different form and differently situated from that usually used.
For these and other reasons I have adopted the method of arranging the
quadrants to stand up from the base instead of depending from the top plate of
the instrument.
In the first place the base plate is supported on three legs with levelling
screens, the legs being sufficiently long to raise the base plate some inches.
Four holes are made in the base plate for the quadrants supports to pass through.
Each quadrant is attached to a brass rod having a terminal at the opposite end
having a short sleeve about the centre of the rod, but of greater diameter. A
rod of ebonite or other insulating material is then taken and a hole bored right
through longitudinally, of such size that the rod will pass freely without touch-
ing the sides, but so that the sleeve on the rod is a tight fit and requires to
be driven gently in. This is done and the arrangement should be such that the
ebonite tube comes up to within half an inch of the under side of the quadrant,
while the brass rod projects at the other end sufficiently to attach the terminal
without touching the ebonite, the outside of the ebonite tube is then corrugated
deeply to increase the insulation.
To support the quadrants with their insulated tubes on the base, a short
sleeve with a screw cut inside and out and with a broad flange on the top is
slipped over each ebonite tube, and is arranged to screw tightly to it, almost in
the centre. The ebonite tube can then be passed through the hole in the base
plate, and the broad flange allows it to stand upright and to be moved about
slightly in any direction required. Another short sleeve flanged and with
female screw cut on it is made which can be slipped over the ebonite rod from
underneath and screws on the top sleeve. The quadrant is then firmly clamped
in its place by friction between the two flanges, but can be adjusted or taken
out altogether by simply unscrewing or taking off the under sleeve. In this
way such a quadrant is very highly insulated and as there is no limit to the
length the ebonite tubes can be made in reason and the rods inside of them,
it follows that any amount of insulation can be obtained.
The surface of the ebonite rods should be carefully washed and cleaned after
being made and they should be dipped while thoroughly dry in paraffin, which
will then keep the surface in perfect condition, as the rods do not require to be
touched in use and are well protected. It is possible to use several ebonite
tubes with sleeves if desired one inside the other, for alternating currents the pre-
cautions need not be taken so specially nor need the tubes be so long.
As regards the quadrants themselves they may be of any known form, but
the form which I prefer as being the simplest and most accessible and at the
same time combining the most advantage is as follows:-
The quadrants are not made in the form of a box as is usual. The lower
quadrants are simply 4 flat plates and the instrument can be used and is very
sensitive with these 4 flat plates in use only, it is obvious that by proper means
the needle can be adjusted at any height above the quadrants and thus the
sensibility can be greatly varied, in addition to the usual methods of discon-
necting more or less quadrants, or varying the charge of the needle.
I however usually prefer to add an upper set of quadrants consisting of
similar flat plates, which, are supported as follows: the lower quadrants have
little brackets projecting outwards beyond their edges from the under side.
The brackets have a square slot cut in their ends, through which a square rod
attached to the upper side of the upper quadrant slides, this square rod is of

page_text: some length, and fits the square slot on the bracket, so that it can be easily
slid up and down, and by means of a thumb screw on the bracket it can be
clamped in any position over a considerable range, or can be brought flat
down on the under quadrant. When the instrument is to be carried about or
sent by rail I lower the needle on the lower quadrants and bring the upper
quadrants down on the top of the needle, which firmly hold it in position with-
out deforming it, and the whole instrument can then be turned over or roughly
used without injury. I make the quadrants to project some distance beyond
the needle, but leave the edges free, so that the needle can be freely inspected
at all times, which is a great advantage in working. If necessary for high
potentials, all the edges of the quadrants can be rounded. I treat thus 3 of
the quadrants, but as regards the fourth in place of the thumb screw I may put
in a pinion with milled head, working in a rack cut in the square rod support-
ing the upper quadrant or I arrange for finer adjustment by screw motion
by which the top quadrant can be raised or lowered after the others are set.
In this way I can bring the needle to zero when charged easily and definitely
without shifting the position of a quadrant as is usually done. If a top set of
quadrants are not used I make one of the bottom similarly adjustable above or
below the level of the other three.
The axis of the pinion I leave square, so that the milled head for adjusting
can be attached from the outside when needed, and then taken off so that
nothing need be disturbed when setting the instrument.
From the base rise 3 rods which support a circular platform a few inches
above the quadrants, the outside case which may be of glass or brass fits
accurately to the outside of the circular platform by means of a brass flange and
at the same time the bottom of the case fits accurately to a rim turned on the
base so as to exclude air or dust. A couple of clamping screws keep the movable
case fixed when travelling.
From the centre of the circular platform above mentioned rises a circular
glass or brass cylinder rather larger in diameter internally than the needle,
and having a flange on the top. This flange carries a brass disc with a groove
in the edge into which a thumb screw arranged horizontally fits, permitting
the disc to be turned round and clamped in any position.
This disc which carries the suspension arrangements has a circular flange
in its centre projecting vertically upwards, and hollow inside. A brass cover
fits over this loosely, having top and sides, and in the sides are four thumb
screws which permit the cover to be moved about and set in any position over a
certain range in order to center the suspension.
This cover carries a block or tube of ebonite suitably grooved to give high
insulation and which carries the suspending arrangements of the needle itself.
These consist of a brass sleeve fixed to the ebonite or other insulating sub-
stance in which works up and down by means of a pinion with ebonite milled
head a long rod, with a rack cut in it, or for simpler forms the rack may be
omitted and sliding friction alone used. A spring presses on the rack to make
contact always, and the lower end of the rack contains the fork for holding
the suspension of the needle as described above. A terminal suitably attached
enables contact to be made with the rack and thus to the needle.
The outer case is provided with a level preferably of the plumb bob type.
A terminal is also placed on the front of the brass base to form the connection
to the case.
If very high insulation is needed, besides the above precautions sulphuric
acid may be carried under the case in three cups attached to the rods which
support the upper part of the instrument. Arrangements can also be made for
supporting the two back quadrants from the two front ones, having thus only
two rods by which the leakage is reduced to half. This same object may also
be obtained by very highly insulating the needle, and in using the instrument

page_text: in what may be called the French method, or the whole instrument may be put
under a large glass bell, when adjusted and this can be kept dry by acid-the
leads from the terminal being brass wire coming through in the base, and having
corks slipped over them, which may be kept in the holes through which they
come till an experiment is made, and then they are slightly withdrawn so as
to leave the wires free. If the bell jar used is supported on three legs at a
height of a few inches from the table, the connections are easily made in this
way and the most perfect insulation can be secured for specific insulation
tests etc.
In order to work such an electrometer a proper key is necessary, particularly
when it is required for alternating and high potential measurements.
Other
forms of key may be employed but I have invented a form of key which gives
special advantages and facilities. The principal of the key is what is called
the double current pattern, and for this principle I make no claim.
The particular pattern I use to attain high insulation and special facilities
in working is as follows:-
The base of the key is a metal plate, mounted on three short legs.
On this base are fixed two columns of ebonite or other insulating material
hollowed out a certain distance down their centres, and having brass rods
screwed into the hollows which are of such a size that the brass rod only touches
the sides at the bottom. These brass rods have terminals at their tops. The
one furthest from the operator is the highest, and has a fork projecting from
it with spring contacts underneath. The points of this fork extend over the
top of two movable pillars. The other fixed pillar which is nearest the operator
has a cross bar with two contacts on it, and is lower than the furthest pillar.
The movable pillars are of the same character as the other two but of inter-
mediate height, and have terminals and contacts on their tops and also a
tongue projecting forwards over the bar of the front pillar. When at their
highest position they make contact one on either side of the bar of the front
pillar. I sometimes enclose all this key in a brass case with aperture at the
side for the connections when making tests in which inductive action from
neighbouring bodies might take place.
The working of the two movable pillars is as follows:-Their lower portion
has a brass ferrule on it, which will slide up and down in a collar fixed to the
brass base. Underneath the base two levers are fixed. The fulcrum of each
lever is free to move horizontally at one end and the lower end of the moving
pillar is pivotted to the lever a little in advance of the fulcrum: intermediate
between the fulcrum and the pivot a spring is attached to the lever and the
other end of the spring being attached to the base in such a manner as to keep
In this the
the lever always pressed up against the underside of the base.
normal position of the lever, the contacts at the top of the movable pillars
press against the fork attached to the back pillar. The end of the lever
opposite the fulcrum carries an ebonite finger plate, and works in a guide in
such a manner that the lever may be pressed down till it brings the tongue
bar on the front pillar.
on the moving pillar into contact with the cross
When released it will return under the influence of the spring to its normal
position. Catches are further provided so that by a slight lateral pressure
the lever may be caused to engage in a catch and remain at the bottom of its
travel and the tongue on the corresponding pillar in contact with the front
terminal, or it may be left in an intermediate position by engaging in another
catch when the tongue will be insulated.
To protect the needle or quadrants from injury when using the instrument
on circuits carrying heavy currents, I have found the best protection is to put
one or more high voltage lamps of 8 candle power in series with them. Such
a lamp will protect the instrument in case of accidental contact against double
the voltage the lamps are intended for. Other forms of high resistance may

page_text: be used but a liquid fuse of the ordinary character I do not find satisfactory
as it is liable to introduce errors.
000
1
T
1000
Improvements in Electrometers and in Keys for Operating the same.
I, GEORGE LEONARD ADDENBROOKE, of 53, Victoria Street, Westminster, in
the County of London, Electrical Engineer, 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 electrometers, and in the keys
used for operating the same. The objects in view are to increase the sensitive-
ness, accuracy and range of such instruments; to facilitate their adjustment
and usage as voltmeters, wattmeters, and ammeters in measuring varying
currents in ordinary works or central stations; to reduce their cost; and adapt
them for transportation.
In the further description of the invention, reference is made to the accom-
panying drawings, in which Fig. 1 is a front elevation of an electrometer
embodying my invention, Fig. 2 is a vertical section of the same, Fig. 3 is
a plan of the instrument omitting the legs, Fig. 4 is a plan on the line A-B
showing the quadrant plates, Fig. 5 is a half plan taken at the same relative
position but showing a modification of the quadrant plates, Fig. 6 is a sectional
elevation through a pair of the quadrant plates shown in Fig. 5 together with
the means for supporting the same, Fig. 7 is a sectional elevation of the key
used for operating the electrometer, and Fig. 8 is a plan of the same.
In these drawings, a is a metal base plate, supported on three legs each
having a levelling screw a¹, the legs being long enough to raise the base several
inches. On the base a four hollow columns of ebonite or other suitable insu-
lating material 6 are mounted and each adapted to receive a brass rod c within,
which rod is either turned with an enlarged portion at some part of its length
to fit tightly in the bore of its corresponding column, or if turned of the same
diameter throughout, each column is bored larger than the rod except at one
portion of its length (conveniently situated at the centre) where it should fit
the rod closely. This is done to provide an air insulation for a large propor-
tion of its length between each rod and its column. The exterior of each column
is also turned with a series of narrow grooves close together as shown, also
for the purpose of surface insulation thus preventing leakage. Suitable means
such as a sleeve and and clamping nut a² are provided for mounting the columns
upon the base a, and a terminal c¹ is conveniently formed upon or secured
to the bottom of each rod c, a short distance below the ebonite column b, to
avoid touching the latter.
Each rod carries a pair (or more) of quadrants, each lower one d being
mounted either directly upon the top of its rod c or upon a bracket forming a
part thereof.
The upper quadrants are sometimes supported by a small
square rod passing through a slot in the bracket beneath and clamped in
its required position by a thumb screw, or mounted directly on a brass rod
extending upward from the brass rod c, which is then made tubular for the
purpose; suitable means for adjustment being provided. It will be seen that the
quadrants are not made in the usual box manner in which the top and bottom
surfaces are fixed rigidly apart, but are made as flat plates capable of adjustment

page_text: between their contiguous surfaces and are even adapted for the upper plates
to be lowered upon the lower ones d, in order to secure the needle from injury
when travelling.
The quadrant plates d and d are shaped and arranged as shown in the plans
Figs. 4 and 5 with a narrow gap between each contiguous pair, in the usual
manner, but sometimes I make them adjustable in a radial direction to and
from the centre, when the instrument is required for high tension currents.
In this case the adjustment is made either by a slide at the quadrants, or by an
enlarged hole in the base a at the sleeves and clamping nut device a², as may
be convenient; the object being to enlarge the air gap symmetrically between
the contiguous quadrants to prevent arcs being formed between them, and to
reduce the gap when the instrument is required for currents of lower potential:
The instrument is adapted for use for some purposes with the lower quadrants
only, the needle being adjustable in relation thereto, but in some cases where
a high degree of sensibility is required I increase the number of quadrant
plates by similarly mounting extra pairs vertically above those shown in
Figs. 1 and 2, adding one or more additional needles, or else increase the
number of plates in plan to form hexagon, octagon or star plates, and making
the needle with an increased number of radial arms to correspond therewith.
The lower portion of the electrometer, about the quadrant plates and their
supports, is enclosed by a cylindrical case e of glass or brass, which is fitted
neatly upon the base a in combination with a rim, flange or recess, and extends
upwards some distance. The case e is made removeable, and if of metal is formed
with glazed openings to observe the needle and for a beam of light to fall upon
and be reflected from the mirrer. An annular metal ring top or circular
platform is fitted to the top of the case e, but sometimes I support this plat-
form by three or more rods a³ rising from the base, and means are provided
for securing the case in position during transit. The annular ring platform f
is adapted to carry a lantern or upper cylindrical case e¹, which again carries
and is covered by a disc plate fi having a central hole, with means fitted
therein for suspending or adjusting the aforesaid needle within the quadrant
plates.
The lantern or upper case e¹ may also be of glass or brass, and its internal
diameter is made larger than the diameter of the needle, to permit the with-
drawal of the latter when the disc plate f', or the upper case el with its disc
plate is removed from the circular plate fas required, according to the arrange-
ment adopted in. fitting the parts together. But for general working it is
convenient to lift the case e from the base a, when access is required to the
interior, a joint f4, Fig. 2, being made for that purpose.
In the central hole of the disc plate f¹ is fitted an ebonite tube g bored and
turned with grooves in a similar manner to that already described for the ebonite
columns b, thus giving high insulation to a metal socket g¹, and long flat rod h
fitted therein. The flat rod h extends above and below the upper and lower
ends of the ebonite tube g, being formed at the top with a knob or terminal,
and at the bottom with screw clamping device for holding the fine wire or
strip used in suspending the needle. The flat rod h has also formed a fine
rack on one edge, and a pinion with thumb milled head h³, engaging with
the rack, is adapted for raising and lowering rod h in the socket g¹, and with
it the suspension point of the needle.
On the disc plate f¹ is mounted a brass worm wheel h³, which supports and
is connected with the aforesaid ebonite tube g, and the other devices named
for carrying the needle. A bearing block for carrying a spindle h* is
secured to the disc plate f¹, engaging with the teeth of the said worm wheel h³.
By means of an ebonite milled head on the outer end of the spindle h, the
latter is turned to rotate the worm wheel h³; thus providing for a rapid cir-
cular adjustment of the needle below on a horizontal plane, in addition to
the vertical adjustment of the needle through the flat rack rod h and pinion Z³.

page_text: A further horizontal adjustment of the suspending portion (or head of the
instrument) is provided by forming a circular groove in the flange 2 of the
disc plate f¹ Fig. 2, and this being formed as a loosely fitting cover to the upper
case e, three or four thumb screws f³ fitted edgeways in the vertical flange
of the top of the case are made to bear upon the flange groove f², and thus
by screwing them in and out adjustment of the plate fi is made to accurately
centre the needle between the quadrant plates below. The constructional
details of this part of the instrument may be greatly varied without affecting
the object or working of the invention according to the material adopted for
the upper case e¹. If of brass, the position and form of the flanges can be
variously shaped and the disc plate f¹ made removeable with great facility.
But if the case e¹ is made of glass, a special metal flange is required to fit its
top and to carry the thumb screws, and this again may require a special flange
on the plate f', with or without the groove above named, to receive the thrust
of the screws f³. In Figs. 1 and 2 however, I have shown that the plate f
can be moved on a horizontal plane for adjustment, or entirely taken off to
withdraw the needle if desired. But for this latter operation, and when upper
plates dare in use, it is necessary to remove or raise one of the said plates
sufficiently to clear the needle from between the upper and lower plates, to
permit the removal of the needle. In Fig. 2 this can be done by unfastening
the clamping screw acting on the square rod c² and raising or withdrawing
the upper plate connected therewith. In Fig. 6 the upper plate can be
lifted against the friction of its supporting rod and swivelled round thereon,
so as to be clear of the needle, thus permitting the disc plate f¹ to be lifted
off after slacking out the screws f³, and removing the needle through the upper
case e. Any change or re-arrangement of the needle, or its suspending wire,
or mirror, or clamping device h¹, can thus be attended to readily, but to further
add to the convenience of manipulating the instrument it is necessary to be able
to remove the lower or main case e. For this purpose a turned joint f is made
in the circular plate f, and the latter being supported and connected rigidly
to the base plate a by means of the rods a³, the case e can be lifted off clear of the
instrument thus permitting freely the above named operations in regard to
the needles, as well as the relative adjustment of the upper plates d to the
lower plates d.
To facilitate this latter operation however, without being obliged to remove
the case e a long ebonite rod de having a milled head passes froni the exterior
of the plate f down into the interior of the case e, (Fig. 1) and is turned with
the same kind of grooves to avoid surface leakage as already described for
the columns b. At the bottom of the rod d² a thread is cut upon it, which
engages with a rack (not shown) formed on the stem of one of the small squaro
rods which carries an upper quadrant plate d', and by turning this rod
an adjustment of the plate is made with reference to the lower one, in order
to establish relative electrical balance or symmetry. The case is also provided:
with a plumb bob a, (Fig. 1) to assist the operator in levelling the instrument,
and it is suspended from a suitable point on the circular plate f.
The needle is made of very thin aluminium which is sometimes corrugated
or indented to produce stiffness, and perforated to reduce its weight. The
ordinary double arm needle is formed like the paddle used on canoes, but this
shape may be varied or multiplied when additional needles or additional plates
are required for increased sensitiveness as already described. The needle i is
attached to a light aluminium wire axis by riveting up the end with a
strengthening washer, or soldering, or other convenient method. Part of the
vertical wire axis is filed flat to receive the mirror, while the upper end
of the wire axis is attached to the suspending fine wire or flattened strip
plating and soldering; or clamping the strip between the split upper end of
the wire axis or forming the latter into a hook like shape and flattening
it upon the suspending wire to clamp the same together, or otherwise. The
by

page_text: upper end is clamped at the point of suspension by the device / as above
stated.
:
After the needle is built and arranged, it is fixed in a clamp with its axis
horizontal and blades vertical, cach of which is in turn immersed in a solution
of caustic soda or potash, or weak hydrochloric acid, to eat away all super-
fluous portions or weight of the needle. By painting lines of wax or varnish
on the needle, strengthening ribs may be formed thereon, and the weight
and thickness of the outer edges and broad portions reduced to any desired
amount, thus also decreasing the momentum of the needle in its oscillations.
By such treatment a needle of the usual size may be made of three grains in
weight, exclusive of the mirror. The suspending wire may be about 7 inches
long of No. 50 standard wire guage, or 0015 in. phosphor bronze wire, and
then flattened; so that when the needle is suitably hung between the con-
tiguous faces of the lower and upper quadrant plates d and d¹, placed one
fifth of an inch apart, coupled up idiostatically, and the electrometer used
as a reflecting instrument, with scale two metres distance, a deflection of three
to five millimetres is obtained, with an E. M. F. of 1 volt applied to the
terminals.
It is further to be noted that by the means provided for adjustment at the top
of the instrument, and worked outside the case, the needle can be lowered to
rest on the bottom quadrant plates d, and one or more of the upper plates d¹
lowered thereon; the instrument is thus readily adapted for transportation;
having a great advantage over other electrometers of the class in this respect.
It is to be understood that in using the electrometer I do not limit myself
to the particular details given of the suspending wire or strip, as the dimen-
sions may be varied to suit the exact purposes for which the instrument is
employed, and wire, or even a fine carbon filament be used for suspending
and electrically connecting the needle to enable it to be charged directly from
its highly insulated support, without using a bath of sulphuric acid as hitherto.
Consequently the needle can be fully charged when using the electrometer
idiostatically or otherwise for measuring alternating currents of high frequency;
nor is error likely to be introduced (as in the case of using sulphuric acid) if
alternating currents of high frequency but low voltage flow through the sus-
pending medium to reach the needle, it being well known that the sensitive-
ness of such instruments is considerably diminished if a wire from the moving
part depends into a liquid, owing to the surface tension thereof.
When the electrometer is used heterostatically a charged jar is not neces-
sarily employed to raise the needle to a high potential, although the jar may
be combined therewith in some cases. For most purposes I use instead a
battery of small cells in series, and this is the more convenient as the instrument
being so sensitive an ample deflection can be obtained with a potential dif-
ference of 1 volt between the quadrants when the needle is charged with
about 30 or 40 volts.
The use of the needle in this way has great advantages, but it introduces the
difficulty that although definite and constant, the controlling force of such a
fine strip as above described is very slight; and unless means are taken to
prevent the needle continuing its oscillations, the use of the instrument would
be tedious. While avoiding mica or metal vanes to bring the needle to rest
sooner than otherwise, I have found by careful experiment that if every precau-
tion is taken to make the needle as light as possible, (such as I have already
described herein), its momentum is so reduced that it comes to rest in a
reasonable time without employing any other damping device, while-in addi-
tion the lightness of the needle improves its sensitiveness.
It is stated above that liquid contact with the needle is unnecessary, and
although I have gained sufficient insulation without drying the interior with
sulphuric acid, yet that, or other suitable absorbent may be introduced within
the case in suitable receptacles if special circumstances require it. The details

page_text: already given of the ebonite columns or tubes indicate the means of avoiding
surface leakage, and as they may be made of almost any length required their
insulating qualities can thus be still further increased. But after the ebonite
tubes are made, they should be carefully washed and cleaned, and dipped while
thoroughly dry in paraffin, to keep their surfaces in perfect condition. In some
cases it may be desirable to use double or treble ebonite tubes or sleeves one
within the other, but for alternating currents such extra precaution is scarcely
required. It will be understood further that all the usual terminals required
are fitted to the instrument, and that the edges of the quadrant plates, or other
metal points requiring it, are suitable rounded.
In working the instrument any suitable key may be employed, but I have
designed a special form which gives high insulation and affords facility in
manipulation as shown in Figs. 7 and 8 In these figures j is a base plate stand-
ing on three legs and carrying four vulcanite columns in a vertical position.
Each of these is bored tubular down to a point near the bottom end, as shown
in section in Fig. 7, and a brass rod is fitted therein in the manner shown so
that it is only in contact with the ebonite at its lower end. The upper end
of each brass rod is provided with a suitable terminal, and sometimes the base
likewise. The back or highest terminal rod carries a forked projection with
a split spring beneath adapted to come in contact with the terminal points
of the two side columns when the latter are raised. Two keys k³ are so pivoted,
one to the lower end of each side column and arranged in a socket at the
lower end that each of the side columns can be lowered in its socket * when
its corresponding key is depressed against the tension of a spring and the
fulcrum end of the key, which bears against the head of a screw fitted in
the base j. In depressing each key thus, an arm m (also having a split spring)
at the top of each side column is carried down with its terminal until it
touches a point on its adjacent end of a double arm mounted on the top of
the front column thus making electrical contact therewith when the key is
depressed, or reversely with one end of the double arm when the key is
liberated through the action of the spring . By manipulating the two keys k
separately in conjunction with the side columns, the latter operate as current
reversers, and by a side detent in the flange of the base j (not shown) the two
keys can be independently held in a neutral position no contacts being made
at the terminal ends. The ebonite columns may be turned with recesses on
their outer surface as previously described for the ebonite columns of the
instrument.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed, I declare that what
I claim is;
1. An electrometer having a raised base a with columns of insulating
material mounted thereon and extending partly above and partly below the
said base, each column containing a metal rod carrying a terminal at its lower
end and one or more quadrant plates at its upper end, combined with an
insulated adjustable tube or head carrying a rod h with means for supporting
a needle depending therefrom and adapted to be influenced when in close
proximity to the said quadrant plates, means for supporting the said tube or
head from the base a, and a case e adapted to be removeable for access to the
said quadrant plates without disturbing the tube g or means for supporting
the needle, substantially as and for the purpose herein described and shown
by the drawings.
2. An electrometer having a raised base a with columns 6 of insulating
material mounted thereon to extend above and below the said base, combined
with a metal rod in each column carrying one or more quadrant plates, an upper
case e¹ and means of supporting the same from the base, a plate f¹ or top to
the said upper case e¹ having means for suspending and adjusting a needle

page_text: depending therefrom, means for placing and clamping the said needle between
an upper and lower quadrant plates, and a lower case e surrounding the said
quadrant plates adapted to be opened or removed to provide access to the said
quadrant plates from the exterior, substantially as and for the purpose herein
described and shown in the drawings.
:
3. An electrometer having a raised base a, a removeable case e, and an
upper case el supported from the said base and carrying an adjustable and
removeable disc plate f¹ and adjustable means thereon for carrying a suspended
needle, the said upper case e¹ being made larger in diameter than the needle
to permit the latter to be withdrawn when the disc plate is removed but smaller
in diameter than the case e to enable the same to be lifted vertically for
access to that part of the interior at which the needle is intended to act, sub-
stantially as and for the purpose herein described and shown in the drawings.
4. In an electrometer the combination of a tube g of insulating material
containing a socket g and rod therein, means such as ' for suspending a
needle therefrom, means for adjusting the rod h vertically, a worm wheel 13
adapted to support the said tube g and means for rotating the same upon a
horizontal plane, and an adjustable disc plate f forming the removeable top
of a case and adapted to carry the said worm wheel, tube, socket and rod, sub-
stantially as and for the purpose herein described and shown in the drawings.
5. In an electrometer, the combination of a lower quadrant plate d, and an
upper quadrant plate d', with means whereby the said plates may be adjusted
towards or from the contiguous faces of the said plates, means for conducting
an electric charge or current thereto, and an insulated support, substantially as
and for the purpose herein described and shown in the drawings.
6. In an electrometer an ebonite or other like insulating support. bored and
adapted to receive an interior metal rod or fitting with an elongated proportion
of air insulation between the two, the said support having also an exterior
elongated surface from its metallic base and adapted to provide a high degree
of insulation, substantially as and for the purpose therein described and shown
with reference to Fig. 6.
7. In an electrometer the combination of a metal base plate with an elon-
gated highly insulating tube mounted centrally thereon, a metal rod fitted
therein with an air space between the two for the greater portion of its length,
a terminal at one end of the said rod, and a quadrant plate at the other, sub-
stantially as and for the purpose herein described and shown in the drawings.
8. In an electrometer, the combination of a lower quadrant plated with an
upper quadrant plate within a case, and means such as for adjusting
from the exterior of the case the distance between the said plates for the purpose
liercin described and shown in the drawings.
9. An electrometer arranged and operating substantially as herein described
and shown in the drawings Figs. 1, 2 and 3.
10. A key for working electrometers having a base with four vertical high
insulation columns and mounted thereon, and having metal terminals
fitted therein and carrying arms k', m and n at their upper ends, and having
two keys for operating the same as and for the purpose herein described and
shown by the drawings Figs. 7 and S.
Tatadh Cl day of Contauch 1900
FAIRFAX & WETTER,
37 and 39, Essex Street, Strand, London, W.C.,
Agents for the Applicant.