An Electrical Geodetic Apparatus

Mining and Scientific Press

AMONG other new things in the mining and scientific world is what is styled an "electric survey." Men have always claimed ability to tell where mineral is located, by surface indications, and it is not strange that, with the new order of things, the old divining rods and "dousing sticks" should be discarded and electricity brought into the effort to indicate the location and course of mineral veins. F. H. Brown of Los Angeles, Cal., has a patented device that he styles an "electro geodetic mineral finder." He furnishes the following explanation of its operation:—

"The instrument used is a modification of the common form of the Wheatstone bridge, the modifications rendering the instrument capable of overcoming the inaccuracies of measurement heretofore caused by earth currents and abnormal resistances set up by electrolysis when battery currents are sent into the earth from a metallic electrode. In using the machine the custom is to make many measurements of the resistances of the same definite length of earth in a given locality. If there are no ore bodies within onehalf of the distance between the electrodes from the surface of the earth, the current will find the path of least resistance in the moist earth nearest below the crust. and close its cuit through that path. Under this condition, all the resistances in the locality will approximate the same. In taking these different measurements, however, should we measure the resistance of a certain definite length of earth underneath which lay a body of ore, less than one-half the distance between the electrodes, from the surface, then the current would find the path of least resistance, in passing down vertically to the ore body to a point nearest the positive electrode or rod, would pass laterally through the ore body to a point nearest the other rod or electrode, then vertically upwards to the other electrode.

"The lateral resistance through the body would show comparatively no resistance, and the reading on the instrument would be only one-half to nine-tenths of the amount indicated on the instrument by the other definite lengths under which there was no ore.

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Let Something Good be Said
September 19, 1901

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