Magnetic surveys are also useful for discovering some types of ores. Delicate magnetic measurements can be made with the help of radio tubes, detecting changes in the direction of the tux of the earth's magnetic field. Deposits of magnetic material such as iron andj nickel usually reveal their presence by very slight deflections in the earth's magnetic lines of force. While these deflections are not discoverable with the ordinary compass, put radio-tube apparatus to work in detecting these minute shifts, and the electronic finger points unmistakably to where the minerals are to be found.
If the prospector is looking for radio-active deposits of any kind such as radium or thorium which are constantly throwing off electron particles, a radio tube detector will quickly announce by a series of loud clicks when the prospector is in the presence of radio-active material Many of our rocks are radio active, and this fact enables the geologist to locate associated minerals.
Such radio-active detectors employ a vacuum tube, into which the high-speed radio-active particles penetrate. Each such penetration Causes the electrical conductivity of the vacuum to break down momentarily and the observer hears a click, Such a detector is known as a Geiger counter, For locating. smaller metallic objects and metal masses underground, some interesting applications of radio detectors have been developed. If it is possible to make an interrupted current flow in the underground object or pipe, a sensitive detector using radio tube amplifiers will be able to pick up the electromagnetic waves, and by moving the detecting instrument around, the location of the underground object can be pretty well established.
If the underground metal object is isolated, such as a metal box or a "pot of gold" it is possible to use a small radio transmitter on the surface to generate waves in the underground object, and these waves from the object can then in turn be picked up by the sensitive receivers.
An M-scope is a sensitive radio-tube device for locating buried treasure, pipes, cables, and other metal objects, by the aid of radio waves, By means of two handrails, the treasure hunter carries a radio transmitter behind him, and a receiver in front of him. With this curious rigging, he paces over the ground which he suspects contains buried treasure or a buried pipe or cable, and when he gets over the buried metal object of the search that object makes itself known by a buzzing in his headphones.
In an American state, the M-scope was used to locate a pistol, said to have been used by a murderer. In New England, the instrument was used after the death of an eccentric old woman, to find a metal box containing stocks and securities which she had hidden in the garden. Once, a group of undertakers wired post-haste to the Fisher Research Laboratories for an M-scope to locate a casket lost underground. Sure that there were valuables from Revolutionary times hidden somewhere on his farm, a New England farmer invested in an M-scope.
Text read from the printed page and cleaned; old type leaves the occasional error.