Radio Broadcast (May-Oct 1922)

204 Radio Broadcast so soon showed. Incidentally, the new idea of using radiated energy, as contrasted to the previous schemes, gives us the reason for the change of name from wireless telegraphy, up to now a proper name for the art, to that of radio communication, indicating that the power used in carrying the message was not due to conduction through the earth's surface, or to magnetic induction, but to energy which was actually shaken free from the transmitting station antenna, and left to travel freely in all directions. maxwell's theory of radiated power The theoretical work of Clerk Maxweii carried out during the period from i860 to 1870 and published in complete form in 1873 showed that energy may be radiated from an electric circuit and that this energy shaken free from the circuit follows the same laws as does ordinary light. In fact, Maxwell made light and radiated electric energy exactly the same kind of a disturbance in the universal ether, Maxwell had, of course, no idea of the usefulness of this startling concept; he was a scientist, of the pure kind as contrasted to the applied, and his work was done in the spirit of pure science. It was the truth regarding certain natural phenomena as he saw it, and it is in the pursuit of the truth about Nature's activities that men like Maxwell pass their lives. Their material reward is generally nil, but that matters to them not at all; the joy of finding out the secrets of nature is the only reward required to keep them stimulated for further work. We shall point out later the work of another pure scientist who predicted theoretically that the modern vacuum tube was possible; others made the tubes and reaped the financial reward. To those buying the tubes to-day it undoubtedly seems that they are still reaping their reward. Maxwell's theory of radiated power was the subject of much scientific argument and discussion; for many years this theory lacked any experimental evidence, either for or against it. The English scientists in general adopted the theory, but those of the continent were against it as being more complex and difficult to understand than the older theories of light and electricity. At the suggestion of von Helmholtz, probably the best known of German physicists, Heinrich Hertz was pursuaded to take up the problem of connecting experimentally the behavior of light and electromagnetic waves. Hertz had almost given up the idea of carrying out this experiment when he noticed a peculiar event taking place in another experiment he was working on. He was discharging a condenser through a spiral inductance coil, when he noticed that another coil in the vicinity produced small sparks every time the discharge took place in the first circuit. This phenomenon is the same as takes place every time a spark transmitter is operated to-day; the current in the antenna of a spark set is excited by theoscillatory discharge in the so-called local circuit. AN ACCIDENT STARTED HERTZ The sparks in the second coil took place with such regularity that Hertz decided to investigate their action. It will be noticed that this beginning of Hertz's remarkable work was the result of accident; if the second coil had not been in the neighborhood of the first when the discharges were taking place, no spark would have been noticed in the second and probably nothing further on the problem would have been done by Hertz and some one else might have carried out his epoch-making work; in fact. Professor Oliver Lodge, in England, would have been almost sure to have carried out the work if Hertz had not started when he did. Hertz's own report of his brilliant and important experiments is available, as the original papers of Hertz have been translated into English and published under the title of "Electric Waves"; for the most part the book is non-mathematical and makes very interesting reading. As Hertz felt his way in this new field his reports had all the fascination of those of the explorer of unknown lands. His various papers followed one another so rapidly that in the space of only two years, 18871889, he had covered practically the whole field and had established firmly the laws of electric wave propagation as we know them to-day. He showed that the waves sent off from an electric circuit carrying high frequency current traveled with the same velocity as does light, that these waves could be reflected by mirrors and refracted by prisms and lenses just the same as light. He measured the length of the waves with which he was experimenting, and found that his detecting circuit must be of the same natural frequency as the transmitter if the response was to be appreciable. As one reads the account of these experiments he feels that Hertz's laboratory was reallx' the birthplace of