. Discovery. Science. 34 DISCOVERY where signals become inaudible, or by introducing another coil into the circuit and noting when its introduction has no effect on the strength of signals, but these are technical details which need not be con- sidered here. This Bellini-Tosi arrangement was used for several years before the war, but was not fully developed until, during the war, the introduction of the three-electrode thermionic tube as an amplifier of weak signals completely revolutionised wireless reception, and made it possible to employ small loop aerials for the reception of signals tran
. Discovery. Science. 34 DISCOVERY where signals become inaudible, or by introducing another coil into the circuit and noting when its introduction has no effect on the strength of signals, but these are technical details which need not be con- sidered here. This Bellini-Tosi arrangement was used for several years before the war, but was not fully developed until, during the war, the introduction of the three-electrode thermionic tube as an amplifier of weak signals completely revolutionised wireless reception, and made it possible to employ small loop aerials for the reception of signals transmitted from even great distances. Small loops are now extensively used for direction-finding purposes in aircraft, and larger ones in ships. The adoption of this apparatus' in ships is not so general as in aircraft, but a few score of our merchant ships are already fitted. The possible errors already mentioned largely account for this comparatively slow growth, as well as the fact that directional shore stations can give more accurate. Fig. 3.—trianguIvAr loop aerials. bearings to ships than ships can obtain with their own directional apparatus. In France, nine of these shore stations are already in operation along the English Channel alone, and in the United States about a hundred are contemplated, of which more than half are working. In this country there are only four in operation. These are at present under Admiralty control, but as has recently been announced in the Press, it is intended to transfer this work to the Post Office, the department responsible for our commercial wireless communications. In shore stations greater accuracy is obtained than in ships, as there are less obstructions to the path of the waves in the form of masts, stays, etc., and more highly trained operators, as well as conveniences in the matter of space, quietness, and stability, are available. A ship or aircraft fitted with directional apparatus can obtain a bearing relative to its fore and af
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