Charles Vernon Boys

“ 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. ”

“ 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.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. ”

“ 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. ”

“ 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. ”

“ 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: Clock-work 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 one wheel, the cylinder goes forward in contact with one and back in contact with another on its opposite side. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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. ”

“ 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 ”

“ 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. ”

“ 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 three pounds, for it takes four to make it go twice as fast. I will hang on nine pounds. One now goes exactly three times as fast as the other. ”

“ 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 around gently. ”