The Electrician (London), August 1, 1902:
As we have frequently announced in our pages, a number of scientists scattered all over the civilised world are eagerly seeking the solution to the problem of wireless telephony. The achievements of Mr. MARCONI and other workers in the field of wireless telegraphy have naturally suggested that, if Morse signals can be transmitted by ether waves, it ought to be practicable to use these waves for the wireless transmission of speech. From time to time, indeed, the report is circulated in the daily Press that some one or other investigator has actually succeeded in transmitting speech across several miles of space. Further inquiry, however, usually elicits the information that the method adopted does not correspond to the Hertzian method employed in wireless telegraphy. In fact, the wireless telephony of these scientists is in no real sense an extension or adaptation of Hertzian telegraphy. It follows quite a different line of research, depending upon entirely different principles. Thus, on Tuesday, the Berlin correspondent of the Standard described the wireless telephony experiments recently carried out by Herr RUHMER, over a distance of 4½ English miles, between an accumulator boat moored off a small islet near Babelsberg and Karsberg, in the Grunewald. Loud and clear speaking is reported to have been heard. The method which Herr RUHMER adopts is essentially optical, and consists in the action upon an electro-optically sensitive body, or "electric eye," of a beam of electric or other powerful light projected from the sending to the transmitting station. The prototype of this method was the so-called photophone, which Prof. GRAHAM BELL invented years ago, in early telephone days. It is stated that in Prof. RUHMER'S experiments a parabolic reflector, only 35 cm. in diameter, has been used, no reflector being employed at the receiving end. Success, however, has encouraged him to extend the range of his researches, and he will shortly repeat the experiments between stations 20 to 25 miles apart, using a reflector of much larger size at each station. We wish him every success; for, in spite of its obvious limitations, this optical method of wireless telephony has its uses, and it certainly is an improvement upon the ordinary heliograph. In military and, possibly, also in naval service work, it may find a field of application; and it is even conceivable that it might be used, in calm waters, between two distant ships or between ship and shore. For island lighthouses, also, it might afford a ready means of communication with the mainland. One of the chief merits of the method is that it can be carried on simultaneously between several pairs of stations within the same area without the possibility of messages interfering or going astray. There are, however, obvious limitations to the use of this method; principally, we may notice, that a clear and uninterrupted straight line, for the passage of the beam of light, must be maintained between the two stations, and the atmosphere must be free of rain or fog. Moreover, the cost of maintaining two powerful beams of artificial light between stations would be prohibitive for the purposes of ordinary commercial messages, and sunlight, of course, could not be relied upon always.
Another method of electrically transmitting speech across space is that employed by Sir WILLIAM PREECE. In this method the speech is transmitted across the intervening space between two parallel aerial wires, one of which acts as a transmitter upon the other as a receiver. A battery and a microphone in the circuit of the transmitting wire, and a telephone in the receiving wire, suffice to complete the simple equipment. But this is scarcely wireless telephony, the amount of aerial wire used being often much greater than the distance over which messages are transmitted. Nevertheless, for routes which cannot readily be spanned by an ordinary wire or cable this method is found to be serviceable and effective. We may note, in passing, that Sir WILLIAM PREECE, who has largely experimented on this system, has never conclusively settled the question as to whether it operates by electromagnetic induction or by the stray return currents through the earth. A very simple re-arrangement of the aerial wires would, in favourable weather, completely settle this interesting point. We trust he will adopt our suggestion at the next opportunity.
Neither of the foregoing methods of wireless telephony bears any real relationship to Marconi telegraphy. Unfortunately, the efforts of scientists to evolve a Hertzian system of wireless telephony, corresponding to Marconi telegraphy, have hitherto been futile. The difficulties are great; some of them appear almost insuperable. Imaginative persons have pictured a state of civilisation in which promiscuous conversation could always be carried on by means of pocket wireless telephones. Prof. AYRTON, for instance, has given us the pathetic picture of a man of those days, who, when unable any longer to call up a colleague in some far-distant country, would then "know that his friend was dead." Wireless telephony will have to make prodigious strides before we can rise to that degree of certitude; even, with the ordinary telephone exchange, it is by no means a safe assumption that a man is dead because he does not answer our call. Peradventure he sleepeth, or is on a journey; but more likely the exchange is not attentive. We publish, as illustrations to one of our articles this week, photographs of the London Wall exchange of the National Telephone Co., taken shortly after the disastrous fire by which this exchange was reduced to a complete wreck. The havoc which was wrought by this calamity, in the deprivation of hundreds of business men of an accustomed and almost imperatively necessary means of communication, is eloquent testimony to the immense advantage which would result from the invention of a wireless telephone system, such as Prof. AYRTON and others have described in language so imaginative. Yet we are compelled to admit that these things belong to fairyland and the world of dreams; not to the matter-of-fact everyday world in which we live. Nothing in existing lines, of research, whether with Hertzian waves or otherwise, gives the slightest warrant for the inference that urban and inter-urban telephony will ever be carried on without the aid of conducting wires. It is, of course, quite true, and as trite as it is true, that we cannot claim to be able to perceive the limits of possible future scientific inventions. But that is not the point. A generation ago no one could foresee the telephone; less than three generations ago the electric telegraph was no more than the idle dream which wireless telephony is to-day. A future generation, therefore, may conceivably accomplish as much in wireless telephony as is dreamed of to-day by visionaries. But if it does, it will be by means of discoveries hitherto not even suspected, and by methods not even the germ of which can be detected in the wireless telegraphy of to-day.