World
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Wireless

The carborundum detector is very simple in construction, and may consists simply of a small carborundum crystal held between two brass springs. It works by virtue of the fact that carborundum has what is termed an unilateral conductivity. Supposing a crystal of carborundum be joined in series with a battery and galvanometer, and the current noted, and the poles of the battery reversed and the current again noted, it will be found that the two currents differ greatly altrough the electro-motive force of the battery has remained unaltered. This shows that for currents in one direction carborundum has a very high resistance and is practically an insulator, but for currents in the reverse direction it is comparatively a good conductor. It will thus be seen that a crystal of carborundum can act as a rectifier and change an oscillatory or alternating current into a direct current. Many crystals beside carborundum posses an unilateral conductivity, but not in such a marked degree. It has also been found that for certain voltages the unilateral conductivity of the crystal is greater than for others, and in practice therefor it is usual to tap the crystal across two points of a potentiometer to the terminals of which a battery is joined. The detector is fairly sensitive and reliable, and is greatly used in the United States.