COMMUNICATION (E. V. A.) General Considerations.—Communication by Hertzian waves is the only practical method of transmitting messages beyond the horizon to recipients whose position is not known or whose position is continually changing. Hence wireless telegraphy and telephony have no rivals for the purpose of communicating with distant ships, aeroplanes, surveyors and explorers. Again, it is characteristic of wireless or radio communication that its waves tend to spread equally in all directions, and thus the mes sages can be made available to all who possess the necessary re ceiving apparatus. Examples of this quality are seen in the modern art of radio broadcasting and in the wireless call for help of a ship in distress. Here again, wireless has no competitor.
On the other hand wireless can give many of the services that have hitherto been rendered by land lines and submarine cables. Thus, in transatlantic telegraphy, wireless has been competing with the ocean cables for about twenty years with gradually in creasing success. In some cases, especially in respect of long distances such as England to Australia, New York and Berlin to South America, the competition of radio with the cable has become very acute during the past three years because the erec tion of the necessary wireless stations requires only an insignifi cant capital outlay compared with that necessary for, say, ten thousand miles of submarine cable. These same considerations of cost often decide whether wireless or cable communication is to be chosen for linking a small island community with the rest of the world.
Wireless communications can be said to comprise every variety of traffic that can be handled by aid of wires. For instance, besides the transmission of Morse signals and of music or speech, wireless stations have been utilized for the transmission of pictures, of signatures, of facsimiles of printed pages and for television. In many cases, the rapidity of wireless transmission to any distance is as rapid as that possible over a few hundred miles of land line, and much faster than that possible through a hundred miles of submarine cable. Hence for work such as telephony, facsimile transmission and television, a wireless circuit accomplishes things that are at present impossible on the transoceanic cables.
Wireless communication has, however, some of the defects of its qualities. Inasmuch as the emissions from a wireless station can be picked up by anyone who provides himself with suitable apparatus, there is little of that secrecy which belongs to com munications which are compelled to pass along a copper wire of which the ends are in private hands. Consequently there is always
a quantity of telegraphic and other traffic which preferably goes by wire. For instance, the London correspondents of foreign newspapers often refuse to transmit their news messages abroad by wireless because, if they do, the news may be printed in rival newspapers at the same moment as in their own. This defect may be overcome to some extent by coding, by very rapid trans mission, or, better, by "scrambling" the messages, i.e., making them unintelligible by aid of automatic mechanical devices at the transmitter, devices which can be used in the reverse sense at the authorized receiving station.
This comparison between wireless and wire will be incomplete unless the troubles that afflict both are mentioned. In the case of cables the chief source of interruption of a service is the breaking or leaking of the cable. Such an injury may take two or more weeks to repair; the only mitigation is to provide a duplicate cable or route. On all the great traffic paths of the globe such duplicates exist, and therefore it is found that the delays affect only relatively small communities. Another trouble afflicting the cable is that arising from magnetic storms; usually this averages only a few hours per annum. The principal troubles that afflict wireless communications are the breakdown of aerials in storms, the failure of machinery or power supply, "atmos pherics" and "fading." The failures of a mechanical nature are often prepared against by duplicating, at least in part, the ma chinery. But for "atmospherics" and "fading" no real remedy has appeared as yet. Fortunately, atmospherics are much less trou blesome with short waves than with long, and fading, on the other hand, is much less frequent with long waves than with short ; and, therefore, in the case of an important wireless link a combination of long and short wave stations, operated from the same telegraph offices, could provide an almost continuous service. Such a combination, designed for distances of, say, four thousand miles, would probably not give quite as continu ous a telegraphic service as a submarine cable and might not be any better financially.