Art. LXV.—Notes on the Conduction of Electricity.
[Read before the Wellington Philosophical Society, July 16, 1870.]
The object of this paper is to controvert a view stated in a paper entitled “The earth of New Zealand a bad Conductor of Electricity, as compared with that of other countries, by F. E. Wright,” in Transactions of the New Zealand Institute, Vol. ii., pp. 226–227. The transmission of electrical currents along the telegraph wires, in some cases after they have become detached from the insulators, and lie on the ground, attributed by Mr. Wright to a peculiarity in the New Zealand soil or rock formation, is explained by the fact of the New Zealand telegraphs being worked on what is technically known as the “open circuit” system, one of the conditions of such system being, that it never occurs to have more than one battery sending its current of electricity along the line at the same time, whereas in Australia the lines are, or at least were, until very recently, worked on the converse of the “open circuit,” viz., the “closed circuit,” one of the conditions of this latter system being that there are a plurality of batteries always sending their currents along the whole length of the line, in their respective circuits, and which by so doing prevent a current passing beyond an earth-fault, thus closing the communication between all stations situated on opposite sides of the fault.
After explaining at length the nature of the two methods of working the telegraph, the author concludes by expressing his opinion that the term
conductor, as applied to the earth in relation to battery currents, is a misnomer. The popular theory is, that if the two poles of a battery be put to earth, at no matter what distance apart—be it but one foot or one thousand miles—that the current flows over the wire from the copper pole of the battery to the earth back through the earth, coming up at the zinc pole through the earth, thus completing the circuit. This is not, however, what actually takes place, as the current which leaves the line at the earth, on the copper side of the battery, is taken into the common stock of electricity (of which the earth is a vast reservoir) at that point, and that the current taken up at the earth plate, on the zinc side of the battery, is in like manner derived.