By MR. C. VERNON BOYS.
The subject of this evening's discourse--"Meters for Power and
Electricity"--is unfortunately, from a lecturer's point of view, one of
extreme difficulty, for it is impossible to fully describe any single
instrument of the class without diving into technical and mathematical
niceties which this audience might well consider more scientific than
entertaining. If, then, in my endeavor to explain these instruments and
the purposes which they are intended to fulfill, in language as simple
and untechnical as possible, I am not as successful as you have a right
to expect, I must ask you to lay some of the blame on my subject and
not all on myself.
I shall at once explain what I mean by the term "meter," and I shall
take the flow of water in a trough as an illustration of my meaning.
If we hang in a trough a weighted board, then, when the water flows
past it, the board will be pushed back; when the current of water is
strong, the board will be pushed back a long way; when the current is
less, it will not be pushed so far; when the water runs the other way,
the board will be pushed the other way. So by observing the position of
the board, we can tell how strong the current of water is at any time.
Now suppose we wish to know, not how strong the current of water is at
this time or at that, but how much water altogether has passed through
the trough during any time, as, for instance, one hour. Then if we have
no better instrument than the weighted board, it will be necessary
to observe its position continuously to keep an exact record of the
corresponding rates at which the water is passing every minute, or
better every second, and to add up all the values obtained. This would,
of course, be a very troublesome process.
There is another kind of instrument which may be used to measure the
flow of the water--a paddle wheel or screw. When the water is flowing
rapidly, the wheel will turn rapidly; when slowly, the wheel will turn
slowly; and when the water flows the other way, the wheel will turn the
other way, so that if we observe how fast the wheel is turning we can
tell how fast the water is flowing. If, now, we wish to know how much
water altogether has passed through the trough, the number of turns of
the wheel, which may be shown by a counter, will at once tell us. There
are, therefore, in the case of water, two kinds of instruments, one
which measures at a time, and the other during a time. The term meter
should be confined to instruments of the second class only.
As with water so with electricity, there are two kinds of measuring
instruments, one of which, the galvanometer, may be taken as a
type, which shows by the position of a magnet how strong a current
of electricity is at a time; and the other which shows how much
electricity has passed during any time. Of the first, which are well
understood, I shall say nothing; the second, the new electric meters
and the corresponding meters for power, are what I have to speak of
to-night. It is hardly necessary for me to mention the object of
making electric meters. Every one who has had to pay his gas bill once
a quarter probably quite appreciates what the electric meters are
going to do, and why they are at the present time attracting so much
attention. So soon as you have electricity laid on in your houses, as
gas and water are laid on now, so soon will a meter of some sort be
necessary, in order that the companies which supply the electricity
may be able to make out their quarterly bills, and refer complaining
customers to the faithful indications of their extravagance in the
mysterious cupboard in which the motor is placed. The urgent necessity
for a good meter has called such a host of inventors into the field,
that a complete account of their labors is more than any one could
hope to give in an hour. Since I am one of this host, I hardly like to
pick out those inventions which I consider of value. I cannot describe
all, I cannot act as a judge and say, these only are worthy of your
attention; and I do not think I should be acting fairly if I were to
describe my own instruments only and ignore those of every one else.
The only way I see out of the difficulty is to speak more particularly
about my own work in this direction, and to speak generally on the work
of others.
I must now ask you to give your attention for a few minutes to a little
abstract geometry. We may represent any changing quantity, as, for
instance, the strength of an electrical current, by a crooked line. For
this purpose we must draw a straight line to represent time, and make
the distance of each point of the crooked line above the straight line
a measure of the strength of the current at the corresponding time.
The size of the figure will then measure the quantity of electricity
that has passed, for the stronger the current is the taller the figure
will be, and the longer it lasts the longer the figure will be; either
cause makes both the quantity of electricity and the size of the figure
greater, and in the same proportion, so the one is a measure of the
other. Now it is not an easy thing to measure the size of a figure;
the distance round it tells nothing; there is, however, a geometrical
method by which its size may be found. Draw another line, with a great
steepness where the figure is tall, and with a less steepness where the
height is less, and with no steepness or horizontal where the figure
has no height. If this is done accurately, the height to which the new
line reaches will measure the size of the figure first drawn; for the
taller the figure is, the steeper the hill will be; the longer the
figure, the longer the hill; either cause makes both the size of the
figure and the height of the hill greater, and in the same proportion;
so the one is a measure of the other, and so, moreover, is the height
of the hill, which can be measured by scale, a measure of the quantity
of electricity that has passed.
[Illustration: FIG. 1]
The first instrument that I made, which I have called a "cart"
integrator, is a machine which, if the lower figure is traced out, will
describe the upper. I will trace a circle; the instrument follows the
curious bracket shaped line that I have already made sufficiently black
to be seen at a distance. The height of the new line measures the size
of the circle; the instrument has squared the circle. This machine
is a thing of mainly theoretical interest; my only object in showing
it is to explain the means by which I have developed a practical and
automatic instrument, of which I shall speak presently. The guiding
principle in the cart integrator is a little three-wheeled cart, whose
front wheel is controlled by the machine. This, of course, is invisible
at a distance, and therefore I have here a large front wheel alone. On
moving this along the table, any twisting of its direction instantly
causes it to deviate from its straight path. Now suppose I do not let
it deviate, but compel it to go straight, then at once a great strain
is put upon the table; which is urged the other way. If the table can
move, it will instantly do so. A table on rollers is inconvenient as
an instrument, let us therefore roll it round into a roller, then on
moving the wheel along it the roller will turn, and the amount by which
it turns will correspond to the height of the second figure drawn by
the cart integrator. If, therefore, the wheel is inclined by a magnet
under the influence of an electric current, or by any other cause, the
whole amount of which we wish to know, then the number of turns of the
rollers will tell us this amount; or to go back to our water analogy,
if we had the weighted board to show current strength, and had not the
paddle wheel to show total quantity, we might use the board to incline
a disk in contact with a roller, and then drag the rollers steadily
along by clockwork. The number of turns of the roller would give the
quantity of water. Instruments that will thus add up continuously
indications at a time, and so find amounts during a time, are called
integrators. The most important application that I have made at present
of the integrator described is what I have called an engine-power
meter. The instrument is on the table, but as it is far too small to
be seen at a distance, I have arranged a large model to illustrate
its action. The object of this machine is to measure how much work an
engine has done during any time, and show the result on a dial, so
that a workman may read it off at once, without having to make any
calculations.
[Illustration: FIG. 2]
[Illustration: FIG. 3]
[Illustration: FIG. 4]
Before I can explain how work is measured, perhaps I had better say
a few words about the meaning of the word "work." Work is done when
pressure overcomes resistance, producing motion. Neither motion nor
pressure alone is work. The two factors, pressure and motion, must
occur together. The work done is found by multiplying the pressure by
the distance moved. In an engine, steam pushes the piston first one
way then the other, overcomes resistance, and does work. To find this
we must multiply the pressure by the motion at every instant, and add
all the products together. This is what the engine power-meter does,
and it shows the continuously growing result on a dial. When the piston
moves, it drags the cylinder along; where the steam presses, the wheel
is inclined. Neither action alone causes the cylinder to turn, but
when they occur together the cylinder turns, and the number of turns
registered on a dial shows with mathematical accuracy how much work has
been done.
In the steam engine work is done in an alternating manner, and it so
happens that this alternating action exactly suits the integrator.
Suppose, however, that the action, whatever it may be, which we wish to
estimate is of a continuous kind, such, for instance, as the continuous
passage of an electric current. Then, if by means of any device we can
suitably incline the wheel, so long as we keep pushing the cylinder
along so long will its rotation measure and indicate the result; but
there must come a time when the end of the cylinder is reached. If then
we drag it back again, instead of going on adding up it will begin to
take off from the result, and the hands on the dial will go backward,
which is clearly wrong. So long as the current continues, so long must
the hands on the dial turn in one direction. This effect is obtained
in the instrument now on the table, the electric energy meter, in this
way. Clockwork causes the cylinder to travel backward and forward by
means of what is called a mangle motion; but instead of moving always
in contact with each wheel, the cylinder goes forward in contact with
one and backward in contact with another on its opposite side. In this
instrument the inclination of the wheels is effected by an arrangement
of coils of wire, the main current passing through two fixed concentric
solenoids, and a shunt current through a great length of fine wire
on a movable solenoid, hanging in the space between the others. The
movable portion has an equal number of turns in opposite directions,
and is therefore unaffected by magnets held near it. The effect of this
arrangement is that the energy of the current--that is, the quantity
multiplied by the force driving it, or the electrical equivalent of
mechanical power--is measured by the slope of the wheels, and the
amount of work done by the current during any time, by the number of
turns of the cylinder, which is registered on a dial. Professors Ayrton
and Perry have devised an instrument which is intended to show the same
thing. They make use of a clock and cause it to go too fast or too slow
by the action of the main on the shunt current; the amount of wrongness
of the clock, and not the time shown, is said to measure the work done
by the current. This method of measuring the electricity by the work
it has done is one which has been proposed to enable the electrical
companies to make out their bills.
The other method is to measure the amount of electricity that has
passed without regard to the work done. There are three lines on which
inventors have worked for this purpose. The first, which has been used
in every laboratory ever since electricity has been understood, is
the chemical method. When electricity passes through a salt solution
it carries metal with it, and deposits it on the plate by which the
electricity leaves the liquid. The amount of metal deposited is a
measure of the quantity of electricity. Mr. Sprague and Mr. Edison
have adopted this method; but as it is impossible to allow the whole
of a strong current to pass through a liquid, the current is divided;
a small proportion only is allowed to pass through. Provided that the
proportion does not vary, and that the metal never has any motions on
its own account, the increase in the weight of one of the metal plates
measures the quantity of electricity.
The next method depends on the use of some sort of integrating machine,
and this being the most obvious method has been attempted by a large
number of inventors. Any machine of this kind is sure to go, and is
sure to indicate something, which will be more nearly a measure of
electricity as the skill of the inventor is greater.
Meters for electricity of the third class are dynamical in their
action, and I believe that what I have called the vibrating meter was
the first of its class. It is well known that a current passing round
iron makes it magnetic. The force which such a magnet exerts is greater
when the current is greater, but it is not simply proportional. If the
current is twice or three times as strong, the force is four times or
nine times as great, or, generally, the force is proportional to the
square of the current. Again, when a body vibrates under the influence
of a controlling force, as a pendulum under the influence of gravity,
four times as much force is necessary to make it vibrate twice as fast,
and nine times to make it vibrate three times as fast; or, generally,
the square of the number measures the force. I will illustrate this
by a model. Here are two sticks nicely balanced on points, and drawn
into a middle position by pieces of tape, to which weights may be
hung. They are identical in every respect. I will now hang a 1 lb.
weight to each tape, and let the pieces of wood swing. They keep time
together absolutely. I will now put 2 lb. on one tape. It is clear that
the corresponding stick is going faster, but certainly not twice as
fast. I will now hang on 4 lb. One stick is going at exactly twice the
pace of the other. To make one go three times as fast it is obviously
useless to put on 3 lb., for it takes four to make it go twice as
fast. I will hang on 9 lb. One now goes exactly three times as fast as
the other. I will now put 4 lb. on the first, and leave the 9 lb. on
the second; the first goes twice while the second goes three times.
If instead of a weight we use electro-magnetic force to control the
vibrations of a body, then twice the current produces four times the
force, four times the force produces twice the rate; three times the
current produces nine times the force, nine times the force produces
three times the rate, and so on; or the rate is directly proportional
to the current strength. There is on the table a working meter made
on this principle. I allow the current that passes through to pass
also through a galvanometer of special construction, so that you can
tell by the position of a spot of light on a scale the strength of the
current. At the present time there is no current; the light is on the
zero of the scale; the meter is at rest. I now allow a current to pass
from a battery of the new Faure-Sellon-Volckmar cells which the Storage
Company have kindly lent me for this occasion. The light moves through
one division on the scale, and the meter has started. I will ask you
to observe its rate of vibration. I will now double the current. This
is indicated by the light moving to the end of the second division on
the scale; the meter vibrates twice as fast. Now the current is three
times as strong, now four times, and so on. You will observe that
the position of the spot of light and the rate of vibration always
correspond. Every vibration of the meter corresponds to a definite
quantity of electricity, and causes a hand on a dial to move on one
step. By looking at the dial, we can see how many vibrations there
have been and therefore how much electricity has passed. Just as the
vibrating sticks in the model in time to come rest, so the vibrating
part of the meter would in time do the same, if it were not kept
going by an impulse automatically given to it when required. Also,
just as the vibrating sticks can be timed to one another by sliding
weights along them, so the vibrating electric meters can be regulated
to one another so that all shall indicate the same value for the same
current, by changing the position or weight of the bobs attached to the
vibrating arm. The other meter of this class, Dr. Hopkinson's, depends
on the fact that centrifugal force is proportional to the square of the
angular velocity. He therefore allows a little motor to drive a shaft
faster and faster, until centrifugal force overcomes electro-magnetic
attraction, when the action of the motor ceases. The number of turns of
the motor is a measure of the quantity of electricity that has passed.
[Illustration: Fig. 5.]
I will now pass on to the measurement of power transmitted by belting.
The transmission of power by a strap is familiar to every one in a
treadle sewing machine or an ordinary lathe. The driving force depends
on the difference in the tightness of the two sides of the belt, and
the power transmitted is equal to this difference multiplied by the
speed; a power meter must, therefore, solve this problem--it must
subtract the tightness of one side from the tightness of the other
side, multiply the difference by the speed at every instant, and add
all the products together, continuously representing the growing amount
on a dial. I shall now show for the first time an instrument that I
have devised, that will do all this in the simplest possible manner.
I have here two wheels connected by a driving band of India-rubber,
round which I have tied every few inches a piece of white silk ribbon.
I shall turn one a little way, and hold the other. The driving force is
indicated by a difference of stretching; the pieces of silk are much
further apart on the tight side than they are on the loose. I shall now
turn the handle, and cause the wheels to revolve; the motion of the
band is visible to all. The India-rubber is traveling faster on the
tight side than on the loose side, nearly twice as fast; this must be
so, for as there is less material on the tight side than on the loose,
there would be a gradual accumulation of the India-rubber round the
driven pulley, if they traveled at the same speed; since there is no
accumulation, the tight side must travel the fastest. Now it may be
shown mathematically that the difference in the speeds is proportional
both to the actual speed and to the driving strain; it is, therefore,
a measure of the power or work being transmitted, and the difference
in the distance traveled is a measure of the work done. I have here a
working machine which shows directly on a dial the amount of work done;
this I will show in action directly. Instead of India-rubber, elastic
steel is used. Since the driving pulley has the velocity of the tight
side, and the driven of the loose side of the belt, the difference in
the number of their turns, if they are of equal size, will measure
the work. This difference I measure by differential gearing which
actuates a hand on a dial. I may turn the handle as fast as I please;
the index does not move, for no work is being done. I may hold the
wheel, and produce a great driving strain; again the index remains at
rest, for no work is being done. I now turn the handle quickly, and
lightly touch the driven wheel with my finger. The resistance, small
though it is, has to be overcome; a minute amount of work is being
done; the index creeps round gently. I will now put more pressure on my
finger, more work is being done, the index is moving faster; whether I
increase the speed or the resistance, the index turns faster; its rate
of motion measures the power, and the distance it has moved, or the
number of turns, measures the work done. That this is so I will show
by experiment. I will wind up in front of a scale a 7 lb. weight; the
hand has turned one-third round. I will now wind a 28 lb weight up the
same height; the hand has turned four-thirds of a turn. There are other
points of a practical nature with regard to this invention which I
cannot now describe.
[Illustration: FIG. 6.]
There is one other class of instruments which I have developed of
which time will let me say very little. The object of this class of
instruments is to divide the speed with which two registrations are
being effected, and continuously record the quotient. In the instrument
on the table two iron cones are caused to rotate in time with the
registrations; a magnetized steel reel hangs on below. This reel turns
about, and runs up or down the cones until it finds a place at which
it can roll at ease. Its position at once indicates the ratio of the
speeds, which will be efficiency, horse-power per hour or one thing
in terms of another. Just as the integrators are derived from the
steering of the ordinary bicycle, so this instrument is derived from
the double steering of the "Otto" bicycle. Though I am afraid that I
have not succeeded in the short time at my disposal in making clear
all the points on which I have touched, yet I hope that I have done
something to remove the very prevalent opinion that meters for power
and electricity do not exist.
[Illustration: FIG. 1.--THE BUILDING SUPPORTED BY SCREWS. (SIDE VIEW.)