Radio broadcast .. (1922-30)

What Everyone Should Know About Radio History By PROF. J. H. MORECROFT PART II A~EW years after the publication of Hertz's work in 1888 the scientific world heard rumors of the experiments of Guglielmo Marconi, then about 20 years old. He had been a student of Physics under Professor Rosa, at the Leghorn Technical School, and had especially made himself acquainted with the work of Professor Righi, who had been making experiments similar to those of Hertz, extending Hertz's work into the region of very short electric waves, about one centimeter long. MARCONI'S METHODS MANY contributions to scientific development have been the result of accident; something strange and unexpected has happened in the course of an experiment and has thus started a keen mind in^search of its significance. But not so with Marconi; it is evident in reading of his early experiments and progress that he had set out, intentionally and with premeditation, to develop the laboratory work of Hertz into a successful scheme of communication. And once having started on the problem he stuck to it with a persistence seldom seen in a scientific worker. His progress was methodical, and followed the line suggested by his experimentation; there are no wonderful jumps in the methods of attacking the problem or in the results achieved. The development brought out by Marconi from 1895 to 1902 is an excellent example of scientific attack and accomplishment; with keen insight as to what was happening, Marconi took the logical steps to increase the distance over which he could carry on signalling and also the certainty of the communication. His enthusiasm and ability steered him clear of the thorny and tedious path which must be trod by many inventors; the British Post Office Department and many prominent scientists gave him assistance and encouragement in carrying out his tests. It was in England that Marconi found the conditions best suited to the development of his new scheme of telegraphy; the British Empire has always been foremost in the development of communications as it is evidently of utmost importance for the close cooperation of its component parts. Until the United States entered the field of worldwide radio the British cables practically controlled the field of international communication. This of course gave to her traders a great advantage over others and enabled them nearly to control world trading. It is no wonder therefore that Marconi was so ably assisted in his development work in England. Its success would give the British Dominions still better control over the world's trade routes. As everyone at all acquainted with radio knows, it involves the generation and radiation of high frequency waves at the transmitting station and some means of detecting them at the receiving station. Marconi started by using at his transmitting station radiators similar to Hertz's, but used at his receiving station a more sensitive indicator than was used by Hertz — a device known as the Branly coherer. The coherer, in the form first used by Marconi, was a small piece of glass tubing with metal terminals in each end, the space between these ends being filled with metallic filings, loosely in contact. It possessed a remarkable property by virtue of which if high frequency voltages were impressed on its terminals the contacts between its particles of metal dust became much more intimate so that the electrical resistance of the device became much less. This effect could be taken advantage of in the scheme of Marconi very well; a battery connected through the coherer could ordinarily force but little current through it because of its high resistance, but when it was affected by the high frequency waves sent out by the transmitting station its resistance fell to a low value and thus the battery could send much more current through it and so ring a bell or operate a printing telegraph, etc. This coherer of Branly, which was considerably im