These are used for the purpose of insuring the perfect insulation of the wires, since but for this the electricity would pass down a damp pole to the earth, and be lost.
Is there any truth in the idea that many persons have, that some principle passes along the telegraphic wires when intelligence is transmitted?
This supposition is wholly erroneous; the word current, as something flowing, conveys a false idea, but we have no other term to express electrical progression.
How can we gain an idea of what really takes place, and of the nature of the influence transmitted?
The earth and all matter are reservoirs of electricity; if we disturb this electricity at Boston by voltaic influence, its pulsations may be felt in Chicago. Suppose the telegraphic wire were a tube, extending from Boston to Chicago, filled with water. Now, if one drop more is forced into it at Boston, a drop must fall out at Chicago, but no drop was caused to pass from Boston to Chicago. Something similar to this occurs in the transmission of electricity.
What was the earliest important industrial application of electricity?
One of the earliest industrial applications of electricity was to the driving of street cars. The first electric railway was installed by Siemens, of Berlin, in 1882; and the system was quickly taken up and brought to a high state of development by American engineers. It is remarkable that the system of traction early adopted is the one generally used in America and Europe until the present date. It consists essentially of (a) a supply of continuous current at five hundred to five hundred and fifty volts, generated in (b) a central powerhouse, and transmitted to the car by means (c) of overhead conductors, whence by contact with a trolley wheel on a pole on the car it is led down to (d) two series-excited motors, which are placed electrically first in series with one another at starting, and then in parallel with one another when a sufficient speed has been attained.
To what well-known electrical machines did this give impetus?
Electric dynamos and motors. All such machines will convert the energy of mechanical motion into that of electricity in motion, or the reverse. The former conversion is done by dynamos, to which power is given by steam-engines or other such prime-movers, and made to generate in conducting circuits alternate or direct currents of electricity. Motors, on the other hand, receive the energy of electrical currents, either alternate or direct, and this produces motion of certain parts of the structure.
The theory of the action of a dynamo was first discovered by Faraday in 1831; it is intimately associated with that of a motor, for the principle of conservation of energy points out that either machine is reversible—that is to say, a dynamo may be used as a motor or a motor as a dynamo, though perhaps not so efficiently as when each fulfills the special function for which it was designed.