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The March of Radio
195
flame. Of course, if the passenger was carried past the station platform as fast, or faster, than the velocity of travel of the light wave he would never know whether the match was lighted or not; the light wave which started from the match when it was struck, would not be able to catch up with the observer, and so evidently could not affect the nerves of his eye. But trains and buses do not travel with such velocities, so we can eliminate that possibility from our discussion.
In so far as motion of the receiver is concerned, therefore, it is evident that there can be no effect on the action of radio waves; receiving a radio signal on a moving bus, or on a mile-a-minute train, is no more wonderful, from the standpoint of radio theory, than if the bus or train were stationary.
it is interesting to note that in some of the experiments in getting radio signals to moving trains, the signals were heard when the
train was in a tunnel, a hundred feet underground. Not very strong, to be sure, but still strong enough to be read. It might be said that the radio waves did not penetrate the ground so deeply but came in from the ends of the tunnel. But we also know that a submerging submarine, even after it has gone 60 feet below the surface still gets audible signals, and there are no tunnel ends for the signal to come through in such a case.
The ordinary theory of radio transmission shows that we can expect a certain amount of penetration of the radio waves into the earth or ocean; it can be predicted how far the waves will penetrate sea water, and the experiments with submarines check the theory. It's very much the same as light going through water; some will get through but most of it is absorbed before the light has penetrated the water very far; just so is the radio wave absorbed in the earth's surface.
Recent tests have proven that communication between moving trains and land stations along the route is now practical, and Edgar Sisson, Jr., is here shown operating the outfit on Lackawanna train Number 3
© Underwood & Underwood
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