Year: 1887

page_text: Date of Application, 19th July, 1887
Complete Left, 18th May, 1888
Complete Accepted, 19th July, 1888
do nereby declare the nature of this invention to
My method of measuring electric currents is founded upon the fact that an electric
current passing through a conductor of electricity generates heat, which heat is carried
away from the conductor by the air in contact with it, thus forming convection currents
in the air.
The velocity of the air currents is proportional to the strength of electric current
in the conductor.
I measure the strength of electric current by introducing any kind of apparatus
suitable for measuring the velocity of air-currents. I do not confine myself to the
use of atmospheric air. I sometimes use hydrogen or other gases.
The
My first object is to adopt means for creating a uniform and steady and powerful
air-current by means of a conductor heated by electricity. The heat which is supplied
by the electric current creates a motive force tending to set up an air current.
resistance caused by fluid friction of the air is the opposing force. When the air
current has acquired a uniform steady velocity, the opposing force of air friction is
equal to the motive power. In order to get a high velocity with small motive power
it is necessary to have a low frictional fluid resistance. The resistance is diminished
If the conductor be near the base of
by allowing a very free circulation to the air.
the instrument the air meets with great friction in passing over the base to get to the
conductor. For this reason I raise the conductor above the base at least an inch or
two. To enable the current of air to be uniform, 1 enclose it in a case to guard it
against external currents of air.
If a spiral be cut out of a circle of paper and it be supported on a pivot at its
centre it will rotate about the vertical axis when placed above a conductor carrying
an electric current. If instead of being pivoted, it be suspended by a wire or fibre,
it will be turned through an angle proportional to the square of the electric current.
This spiral may be advantageously enclosed in a cylinder, of slightly larger diameter
than itself, to direct the currents of air, and the whole apparatus may then be put

page_text: under a glass shade. If a pointer be attached to the revolving part the pointer will
indicate on a fixed divided circular scale, the strength of the current.
A convenient form of apparatus for measuring the air currents consists of a cork
with vanes of mica fixed at an angle of 45° to the axis of the cork, cuts being made
on the circumference of the cork for this purpose.
1 prefer however to make the measuring apparatus out of a circular disc of mica
about two and a half inches diameter. Ten corks, or pieces of pith (more or less) are
fixed, by cuts in the corks, to the periphery of the mica circle. Mica vanes, inclined
at an angle of 45° to the mica circle, are fixed one to each cork.
The whole is suspended at its centre by a fine wire of silver, glass, or by a double
fibre, and from the centre hangs down a wire and horizontal pointer which points to
divisions on a circular scale on the base of the instrument, or instead of the pointer a
mirror and scale may be used in the ordinary manner.
An
The electric conductor consists of a circular wire capable of conducting electricity
being slit at one place so as to leave two ends, which are attached metallically to
binding screws which form the terminals of the apparatus. The circular wire is
supported preferably at its two ends and, at its middle. It is placed close below
the vanes and some distance above the base board of the apparatus so as to allow free
circulation of the air. The conductor is sometimes made of a flat spiral so that the
radial width of the spiral is about the same as the radial width of the vanes.
inclosing cylinder is not required for directing the air currents when this apparatus is
used, but a glass or other shade covers the whole apparatus. The divided circle may
be divided so that the pointer will indicate the current directly, or it may conveniently
be divided into 100 parts so that a deflection of more than one revolution may be
noted, a table of values being in this case provided for converting the readings into
the values of the electric current.
When it is required to measure very small currents the conductor may have a high
resistance and may be made of wire wound in many turns, the two ends of the
wire being attached to the binding screws, or it may be made of a comparatively
bad conductor such as carbon mixed with gum or clay. When the conductor has a
high resistance the instrument may be used for measuring differences of electrical
potential.
When I wish to measure the total quantity of electricity which has passed through
the conductor in any time, I mount the revolving part upon a delicate spindle pivotted
at the two ends and carrying a pinion or wheel which gears into wheel work of such
proportions as to give convenient means of reading off the number of revolutions
of the vanes, as in anemometers, gas meters etc. The number of revolutions so
read off is a measure of the total quantity of electricity which has passed through
the conductor.
I prefer however, to use the mica disc and vanes, described above, without any
enclosing cylinder to direct the air-currents. In this case I prefer to pivot the
revolving part at only one point. To do this I cut a circular hole, say half an inch
diameter, in the centre of the mica disc and I fit into the hole a paper coné, about
one inch high, and fix it there by shellac, or by any convenient means. The top of
the cone is fixed to a minute ring of aluminium which is attached to the bottom of a
pinion which is hollow and carries a ruby cup, such as those used for ship's or other
compasses, in the hole of the pinion. This cup rests upon a hard steel point fixed
vertically on a pillar rising from the base of the apparatus.
The rotating part is now quite free to rotate. The pinion gears into suitable wheel
work, the first wheel being at the same level as the steel point supporting the ruby
cup. The rotating part so made weighs only about twelve grains. The mica disc
may be replaced by aluminium wires running from the pinion to the corks supporting
the vanes or the corks may be fixed on a ring of aluminium which is attached by
threads to the pinion containing the ruby cup. On the base board is placed a metal
base carrying the central pillar with the steel point at its top, and also two pillars for
supporting the wheel work. The base board also carries three brass pillars for
supporting the circular conductor. Two of these may be used as connections to the

page_text: terminal binding screws. Two or more of the wheels which move most slowly carry
pointers pointing to divisions on circular dials. It is convenient in some cases to
arrange this in such a manner that the most quickly moving pointer passes over one
division of its dial when one Ampére-hour of current has passed through the
conductor. The same indication will be given when one Ampere has been used
for one hour or two Amperes for half an hour, or half an Ampere for two
hours.
When this apparatus is used as an electricity meter in a distribution on the parallel
system at constant potential, if there were no friction in the solid parts of the
apparatus it would act with absolute truth, but, besides the air friction which varies
as the square of the velocity of the air current, we have also the constant friction of
the pivot and wheel gearing. This is unimportant when the range of currents to be
measured is not large. When this range is large I introduce a constant source of
heat nearly sufficient to overcome the constant friction and nearly sufficient to start
the apparatus. To obtain this constant source of heat 1 employ, besides the main
conductor hitherto spoken of and which is generally of low resistance, a second
conductor placed close to it of very high resistance. I connect the two ends of this
conductor with the two wires outside the apparatus, which are at a constant difference
of potential, and I arrange the resistance of this second conductor so that with the
constant difference of potentials the vanes do not quite begin to move. Any current
passing through the main conductor will now start the vanes, and by this means the
resistance of the main conductor may be much reduced and it will act correctly over
a great range of currents.
A maintaining force might be applied mechanically to the train of counting
wheels.
If the system of distribution be a series one, with constant current, I make the
thicker conductor of so low a resistance that the constant current passing through it
barely suffices to move the vanes. I then choose such a resistance for the other
conductor as enables me to include the whole range of potentials of the system of
distribution. The wheel gearing may now be arranged to read volt-hours. If the
range is not large and the distribution he in series I use only one conductor, viz.: the
one of high resistance.
11
2 T
1007
CARPMAEL & Co.,
Agents for the Applicant.

page_text: Improvements in Meters or Apparatus for Measuring Electricity.
I, Professor GEORGE FORBES, of 34 Great George Street, Westminster, 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 method of measuring electric currents is founded upon the fact that an electric
current passing through a conductor of electricity generates heat, which heat is
carried away from the conductor by the air in contact with it, thus forming convection
currents in the air.
The velocity of the air currents is proportional to the strength of electric current in
the conductor.
I measure the strength of electric current by introducing any kind of apparatus
suitable for measuring the velocity of air currents. I do not confine myself to the
use of atmospheric air. I sometimes use hydrogen or other gases.
My first object is to adopt means for creating a uniform and steady and powerful
air-current by means of a conductor heated by electricity. The heat which is supplied
by the electric current creates a motive force tending to set up an air current. The
resistance caused by fluid friction of the air is the opposing force.
When the air
current has acquired a uniform steady velocity the opposing force of air-friction is
equal to the motive power. In order to get a high velocity with small motive power
it is necessary to have a low frictional fluid resistance. The resistance is diminished
by allowing a very free circulation to the air. If the conductor be near the base of
the instrument the air meets with great friction in passing over the base to get to the
conductor. For this reason I raise the conductor above the base at least an inch or
two. To enable the current of air to be uniform I enclose it in a case to guard it
against external currents of air.
If a spiral be cut out of a circle of paper and it be supported on a pivot at its
centre it will rotate about the vertical axis when placed above a conductor carrying
an electric current. If instead of being pivoted, it be suspended by a wire or fibre,
it will be turned through an angle proportional to the square of the electric current.
This spiral may be advantageously enclosed in a cylinder of slightly larger diameter
than itself, to direct the currents of air, and the whole apparatus may then be
put under a glass shade. If a pointer be attached to the revolving part the
pointer will indicate on a fixed divided circular scale, the strength of the current.
A convenient form of apparatus for measuring the air currents consists of a cork
with vanes of mica fixed at an angle of 45° to the axis of the cork cuts being made
on the circumference of the cork for this purpose.
I prefer however to make the measuring apparatus out of a circular disc of mica
about two and a half inches diameter. Ten corks, or pieces of pith (more or less) are
fixed, by cuts in the corks, to the periphery of the mica circle. Mica vanes, inclined
at an angle of 45° to the mica circle, are fixed one to each cork.

page_text: The whole is suspended at its centre by a fine wire of silver, glass, or by a double
fibre, and from the centre hangs down a wire and horizontal pointer which points to
divisions on a circular scale on the base of the instrument, or instead of the pointer a
mirror and scale may be used in the ordinary manner.
The electric conductor consists of a circular wire capable of conducting electricity
being slit at one place so as to leave two ends, which are attached metallically to
binding screws which form the terminals of the apparatus. The circular wire is
supported preferably at its two ends and at its middle. It is placed close below the
vanes and some distance above the base board of the apparatus-so as to allow free
circulation of the air. The conductor is sometimes made of a flat spiral so that the
radial width of the spiral is about the same as the radial width of the vanes.
An
inclosing cylinder is not required for directing the air currents when this apparatus is
used, but a glass or other shade covers the whole apparatus. The divided circle may
be divided so that the pointer will indicate the current directly, or it may conveniently
be divided into 100 parts so that a deflection of more than one revolution may be
noted, a table of values being in this case provided for converting the readings into
the values of the electric current.
When it is required to measure very small currents the conductor may have a high
resistance and may be made of wire wound in many turns, the two ends of the wire
being attached to the binding screws, or it may be made of a comparatively bad
conductor such as carbon mixed with gum or clay. When the conductor has a high
resistance the instrument may be used for measuring differences of electric
potential.
When I wish to measure the total quantity of electricity which has passed through
the conductor in any time, I mount the revolving part upon a delicate spindle
pivoted at the two ends and carrying a pinion or wheel which gears into wheel
work of such proportions as to give convenient means of reading off the number
of revolutions of the vanes, as in anemometers, gas meters, &c. The number of
revolutions so read off is a measure of the total quantity of electricity which has
passed through the conductor.
I prefer however, to use the mica disc and vanes described above without any
enclosing cylinder to direct the air-currents. In this case I prefer to pivot the
revolving part at only one point. To do this I cut a circular hole, say half an inch
diameter, in the centre of the mica disc and I fit into the hole a paper cone, about
one inch high, and fix it there by shellac or by any convenient means. The top of the
cone is fixed to a minute ring of aluminium which is attached to the bottom of a
pinion which is hollow and carries a ruby cup, such as those used for ship's or other
compasses, in the hole of the pinion. This cup rests upon a hard steel point fixed
vertically on a pillar rising from the base of the apparatus.
The rotating part is now quite free to rotate. The pinion gears into suitable wheel
work, the first wheel being at the same level as the steel point supporting the ruby
cup. The rotating part so made weighs only about twelve grains. The mica disc
may be replaced by aluminium wires running from the pinion to the corks supporting
the vanes or the corks may be fixed on a ring of aluminium which is attached by
threads to the pinion containing the ruby cup. On the base board is placed a metal
base carrying the central pillar with the steel point at its top, and also two pillars for
supporting the wheel work. The base board also carries three brass pillars for
supporting the circular conductor. Two of these may be used as connections to the
terminal binding screws. Two or more of the wheels which move most slowly carry
pointers pointing to divisions on circular dials. It is convenient in some cases to
arrange this in such a manner that the most quickly-moving pointer passes over one
division of its dial when one Ampére-hour of current has passed through the
conductor. The same indication will be given when one Ampére has been used for
one hour or two Ampéres for half an hour, or half an Ampére for two hours.
When this apparatus is used as an electricity meter in a distribution on the parallel
system at constant potential if there were no friction in the solid parts of the apparatus
it would act with absolute truth, but, besides the air friction which varies as the square

page_text: of the velocity of the air current, we have also the constant friction of the pivot and
wheel gearing. This is unimportant when the range of currents to be measured is
not large. When this range is large I introduce a constant source of heat nearly
sufficient to overcome the constant friction and nearly sufficient to start the
apparatus. To obtain this constant source of heat 1 employ, besides the main
conductor bitherto spoken of and which is generally of low resistance, a second
conductor placed close to it, of very high resistance. I connect the two ends of this
conductor with the two wires outside the apparatus, which are at a constant difference
of potential, and I arrange the resistance of this second conductor so that with the
constant difference of potentials the vanes do not quite begin to move. Any current
passing through the main conductor will now start the vanes, and by this means the
resistance of the main conductor may be much reduced and it will act correctly over
a great range of currents. A maintaining force might be applied mechanically to the
train of counting wheels.
If the system of distribution be a series one, with constant current, I make the
thicker conductor of so low a resistance that the constant current passing through it
barely suffices to move the vanes. I then choose such a resistance for the other
conductor as enables me to include the whole range of potentials of the system of
distribution.
The wheel gearing may now be arranged to read volt hours. If the range is not
large and the distribution be in series I use only one conductor, viz., the one of high
resistance.
Having now clearly defined and set forth the nature of my invention I will now
refer to the drawings which show the details of the various parts of my invention.
Figures 1 to 4 shew the apparatus arranged for measuring the strength of the
current.
Figures 5 to 11 show the application of counting apparatus to the wheelwork.
Figure 1 is a perspective view of one form of the apparatus. A is a base board.
B. B. B. are three columns supporting a glass cylinder S. C is a glass shade
enclosing the apparatus. D is a clip on the top of the glass shade for holding a silver
wire E or for a bifilar suspension. The lower end of this wire is attached to the centre
of a paper spiral F. This is made by taking a disc of paper G, and cutting it in a
spiral as shown by the line on G. His a conductor of electricity attached at its ends
to the binding screws K K. L is a pointer and M is a divided circle.
Figure 2 is another type of vane consisting of a cork A with four mica vanes B B
fitted in slots at an angle of 45°. C is a glass or other fibre fixed to the centre of the
cork. D is a fine silver wire. E is the pointer. The other parts of the arrangement
are as in Figure 1.
Figure 3 is an elevation of the arrangement I prefer. A is the fine silver wire
attached to a cork B. C is a wire of aluminium also attached to the cork B and
carrying the pointer D. E, E, is the divided circle. F, F, is the conductor.
G G are the binding screws attached to the end supports of F. H is a disc of mica
with ten corks fixed equally on its edge. L L are vanes of mica, inclined at 45°, fixed
to the corks. The external diameter of the whole is four inches.
Figure 4 shows another form of conductor which may be used. It is a zig zag of
metal on a wooden frame.
The dimensions of the conductor depend altogether on the strength of current it is
required to measure. Many forms of conductor may be used, but I prefer the spiral
form of conductor shewn by Figure 4*, or a conductor formed of two concentric
circles of wire joined by several others in the manner shewn at Figure 4**.
Figures 5 to 11 illustrate the applications of counting apparatus to the apparatus of
Figure 3.
In these drawings the same letters apply to the same parts. Figure 5 is a
sectional elevation.
Figure 6 is a plan of the instrument.
Figure 7 shews a plan of the dials.
Figure 8 shews, the positions of the wheels and pinions, the teeth and leaves of

page_text: which are not indicated since their number depends upon the purpose to which the
instrument is to be applied.
Figure 9 shows details of the three most quickly moving wheels, and
Figure 10 of the three wheels of slowest motion.
Figure 11 shews an arrangement to prevent injury in transport.
A is a base board. B is a cylinder of brass with a glass top to form the case.
D is a metal base screwed to the base board. E E are two metal pillars attached to
the base D. F is a brass bar screwed to the tops of the pillars. A little play is
allowed in one of these screws to adjust the depth of the gearing of the pinion attached
to the vanes.
When adjusted it is then fixed. G G are two pillars attached to the
brass bar F, and carrying the bar H. K K are two pillars also screwed to F and
carrying the bar L. M N are steel plates to support the lower ends of the pivots of
the wheel. The arrangement of wheels and pinions may be as shown in Figures 8, 9
and 10, each wheel may have 80 teeth and each pinion may have eight leaves.
P. Q, is the double dial. R S are the two pointers. a is a pin screwed into the metal
base with a hard steel point at the top. 6 is the circular disc of mica, c the corks at
its periphery and d the vanes. e is the paper cone fastened to the mica disc. fis
the pinion of eight teeth which contains a ruby cup to rest on the steel point. g is a
cylinder of wood sliding on the pin a, having a shoulder at the top to catch the cone e,
and press the top of the pinion against a stop h which is fixed to the metal plate F.
This prevents injury in travelling. The cylinder of wood g has a slot k in which
the fork I cut in a metal spring m, plays (Figure 11). The spring m rests on a piece
of metal or wood, n, to which it can be screwed by the screw p. q is the conductor
which may be of any suitable metal as iron or copper half an inch wide, bent on a
circle, and of such thickness as to give a resistance of one tenth of an ohm. It is
supported by three brass or copper pillars 7.
Two of these are at the ends of tho
If made as
conductor and are attached by metal strips s. s. to the terminals t t.
described, the mica vanes enclosing a circle of a diameter of four inches, one division
of the dial corresponds to about one ampére hour.
A final adjustment may be made by altering the resistance of the conductor by
cutting it, or by altering the air friction by putting obstructions to the free circulation
of the air current, or by altering the position of the conductor.
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 instrument for measuring electricity the combination of a conductor heated
by an electric current and so arranged as to generate a current in air or gas; with
apparatus indicating the velocity of the said current.
2. In an instrument formed in the above manner for measuring electricity making
the electric conductor of the forms shewn at Figures 4* or 4**.
3. In an instrument for measuring electricity the combination of a conductor
heated by an electric current and light vanes tending to rotate in an air or gas current
generated by the heat but restrained by one or more fibres wires or springs substantially
as described.
4. Apparatus substantially as described for measuring the force of electric currents.
5. In an instrument for measuring electricity the combination of a conductor heated
by an electric current; light vanes rotating in an air or gas current generated by the
heat;
and a counting train connected with the vanes substantially as described.
6. Apparatus substantially as described for measuring and indicating the quantity
of electricity flowing in a circuit in a given time.