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Updated: June 20, 2025
I remember distinctly when Mr. Edison gave me the problem of placing a motor in circuit in multiple arc with a fixed resistance; and I had to work out the problem entirely, as I could find no prior solution. There was nothing I could find bearing upon the counter electromotive force of the armature, and the effect of the resistance of the armature on the work given out by the armature.
A further convenience arising from electromotive power is the absence of combustibles and the absence of the products of combustion-matters of great importance; and for the milder seasons, when inland navigation is principally enjoyed, the absence of heat, smell, and noise, and, finally, the dispensing with one attendant on board, whose wages, in most cases, amount to as much or more than the cost of fuel, besides the inconvenience of carrying an additional individual.
It implies either that the machine is CAPABLE OF INCREASING ITS OWN ELECTROMOTIVE FORCE NINE TIMES WITHOUT AN INCREASED EXPENDITURE OF POWER, or that external resistance is NOT resistance to the current induced in the Edison machine. "Does Mr. If so Mr. Edison has discovered something MORE than perpetual motion, and Mr. Keely had better retire from the field.
The enormous use of both step-up and step-down transformers transformers which respectively induce currents of higher and of lower electromotive forces in their secondary coils than are passed through their primaries shows the great practical value of this invention.
That is, by dividing the resistance of the circuit in ohms, by the electromotive force of the current you will get the amperes flowing in the circuit. Finally if you know what the resistance of the circuit is in ohms and the current is in amperes then you can find what the electromotive force is in volts since: Ohms x Amperes = Volts, or R x I = E
Thus one is led, from theoretical and practical considerations, to the use of high frequencies, and this means high electromotive forces and small currents in the primary. When he works with condenser charges and they are the only means up to the present known for reaching these extreme frequencies he gets to electromotive forces of several thousands of volts per turn of the primary.
The unit of electromotive force is the volt, and this is the electric pressure which will force a current of 1 ampere through a resistance of 1 ohm; it is expressed by the symbol E. A fresh dry cell will deliver a current of about 1.5 volts. Resistance and the Ohm.
That is rather small compared with the Professor's result. Rossetti found that the current is nearly proportional to the velocity of rotation. It increases a little faster than the velocity. The electromotive force and resistance is constant if the velocity is constant.
When the electrical pressure was normal, neither lamp was lighted; but if the electromotive force rose above a predetermined amount by one or two volts, the red lamp lighted up, and the attendant at the hand-wheel of the field regulator inserted resistance in the field circuit, whereas, if the blue lamp lighted, resistance was cut out until the pressure was raised to normal.
The Paris Congress decided upon adopting certain units of resistance of electromotive force, of current, and of quantity, and they determined the particular length of a column of mercury that should represent the ohm a column of mercury 106 centimeters long and of one square millimeter in section.
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