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Updated: June 20, 2025
At this end of the line I merely measure the electromotive force developed by the difference in temperature of two similar thermo- electric junctions, opposed. We call those junctions in a thermopile 'couples, and by getting the recording instruments sensitive enough, we can measure one one-thousandth of a degree. "Becquerel was the first, I believe, to use this property.
Just as water flowing through a pipe has quantity and pressure back of it and the pipe offers friction to it which tends to hold back the water, so, likewise, does electricity flowing in a circuit have: quantity, or current strength, or just current, as it is called for short, or amperage, and pressure, or potential difference, or electromotive force, or voltage, as it is variously called, and the wire, or circuit, in which the current is flowing has resistance which tends to hold back the current.
The solenoid, S, is interposed in the general circuit, being connected on the one hand with the line, L, and on the other with a very constant battery of an electromotive force proportioned to the resistance of the circuit. Through the electrode that remains free, the battery is grounded with so great care that no variation in resistance can be produced thereby.
Water Valve Analogue of Electric Resistance. A- a valve limits the flow of water. What Ohm's Law Is. If, now, you know what the current flowing in a circuit is in amperes, and the electromotive force, or pressure, is in volts, you can then easily find what the resistance is in ohms of the circuit in which the current is flowing by this formula: Volts E = Ohms, or = R Amperes I
Of what elements shall this constant battery be formed? Mr. Gime recommends the use of the Latimer-Clark elements. Every one knows that the Latimer-Clark element is now the best standard of electromotive force; but let us not forget that this is on condition of its being employed in open circuit.
That is, if you multiply the resistance of the circuit in ohms by the current in amperes the result will give you the electromotive force in volts. From this you will see that if you know the value of any two of the constants you can find the value of the unknown constant by a simple arithmetical process.
Dr. de la Rue concluded his interesting discourse by exhibiting some of the finest tubes of his numerous and unsurpassed collection. Engineering Coulomb's torsion balance has been adapted by M. Baille to the measurement of low electromotive forces in a very successful manner, and has been found preferable by him to the delicate electrometers of Sir W. Thomson.
The furnace at present in use is charged in substantially the same manner, and the current is supplied by a Brush machine of variable electromotive force driven by an equivalent of forty horse power.
This is the "compound-wound" machine, in which the magnets are wound partly in shunt and partly in series with the armature, in such a manner that the strength of the field-magnets and the electromotive force of the current do not vary much, whatever be the number of lamps in circuit.
I think the person receiving that charge would not need another. According to Ohm's law, the strength of current is proportional to the electromotive force divided by the total resistance, external and internal. The last is a very important element in the Holtz machine, and will make a big difference in the current strength.
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