The Electrician (London), January 28, 1898, pages 452-453:
HERTZIAN TELEGRAPHY AT THE PHYSICAL SOCIETY.
For reasons which are fairly obvious, the Physical Society is not remarkable for overcrowded meetings, but on Friday last the Society and its visitors taxed to the utmost the accommodation of the Chemical Society's room in Burlington House. The occasion was to hear Prof. OLIVER LODGE'S discourse on "Wireless Telegraphy," as the new telegraphy is popularly termed. An unannounced event opened the proceedings, when Prof. FITZGERALD exhibited some photographs, sent by Mr. TOLVER PRESTON, showing the spectra of zinc, cadmium and iron, exhibiting the Zeeman effect. The action of the magnetic field on different lines varied considerably, and in some cases where a triple line should appear a doublet was seen or a quadruplet, the two inner members or which were comparatively faint. Arguing on the generally-accepted theory of the Zeeman effect, the varying action of the field on different lines can scarcely be due to difference of amplitude, except indirectly, or in so far as the amplitude depends upon the mass of that portion of the atom which takes part in the vibration corresponding to the particular line. In applying, however, any results based upon the preliminary assumption of a comparatively simple vibrating system, it must be remembered that the iron atom is not likely to be a very simple affair, or it would not have so many distinct periods of vibrations as are indicated by the number of the lines in its spectrum. The whole question of the revolution of the electrically-charged atom or of the charge on the atom has acquired increased interest in another direction by Prof. FLEMING'S hypothesis as to the structure of the ferromagnetic molecule. But this takes us quite beyond the range of the Physical Society's meeting, and of the subject of Hertzian signalling.
After drily remarking that the public seem to think they want "wireless telegraphy," Prof. LODGE said that in 1894 he had not considered it likely his researches would have any practical value in this direction. Incidentally, he mentioned that the title given to his Paper on the agenda was incorrect; he had proposed "Signalling without Connecting Wires"--one of the best names yet suggested for the erroneously-termed "wireless telegraphy." As to the practical applications, there were occasions when one wanted to "shout to the world"--as in distributing political speeches to the Press--and for such a purpose the Hertz-wave and the coherer might be of service. But did not Prof. LODGE forget that no one wants to pay for shouting to the world on a system by which it would be impossible to prevent non-subscribers from benefitting gratuitously? In respect of practical signalling, the whole matter is to arrange some way in which there can be a sufficient degree of "tuning." Prof. LODGE'S exposition of the conditions that an apparatus must comply with to be able to permit of this was a good example of the scientific rather than the haphazard method of invention. The first thing needful is to have a persistent vibration to which to tune, and not one that dies off rapidly and irregularly. This at once excludes the simple RIGHI transmitter. To get persistency, capacity is necessary; the period can be altered by varying either capacity or self-induction. Prof. LODGE introduces both into his system, and tunes with the latter. The coherer is connected up with the resonator in such a way as not to damp the vibrations, but to take the overflow when resonance is set up. The receiver is therefore a real resonator, and not a mere collector of vibrations. The receiver closely resembles the transmitter, except, of course, that the spark gap is removed from the former; the most markedly novel feature is the coil of copper introduced between the two triangular wings. An incidental result of the method of tuning is that the waves used are over 80 yards long. From one point of view this ought to be no disadvantage, since the "shadow" of any obstacle of moderate size would be so much the shorter. In fact, the Hertz-wave would bend round behind it as much as a sound-wave does. Once upon a time Prof. LODGE used to work with 8in. waves. The length of Mr. MARCONI'S waves was about 4ft. On the other hand, it appears that little has been done in the way of getting a plane wave-front--in other words, sending signals in a specific direction. The dimensions of a reflector such as would be required to work effectively with waves 90ft. in length would seem startlingly large, and any method of directing them other than by reflection does not appear hopeful.
It was laid down by a famous bishop, of splendid memory, that a needle could support upon its point eleven angels. There certainly seems mystery and virtue enough in a needle's point to lend probability to the truth of the bishop's dictum. Prof. LODGE tells us that the coherer may advantageously be reduced to a single contact--i.e., that a needle pressed against a flat spring is, of all coherers, the most sensitive, and that it possesses the further merit of requiring no mechanical "tapping-back." Who then, we may ask, would suffer the pangs of questioned priority, the difficulties of adjustment, and the doubtful working of a mass of filings, when better things may be attained with a bare bodkin? The needle-point coherer, however, has its drawbacks, one of which is that in certain conditions it is too sensitive; but in suitable circumstances it may be made to give better results than a Branly tube. In fact, the single-contact coherer works best with what Prof. LODGE called "electrical tapping-back." The resistance-change produced by the oscillations is found to be almost simply proportional to the power of the received Hertz-waves; moreover, a weaker discharge following a stronger is able nearly to restore the resistance to its first value. If our memory serves us aright, an effect akin to this was observed about ten years ago by Prof. MINCHIN, in relation to his photo-electric cells. One of these cells, under certain conditions, became insensitive to solar radiations, and its sensitiveness could be restored in one of two ways, namely, either by mechanical or acoustical tapping of the cell or its support, or by connecting a small battery of a few volts to the electrodes of the cell. It is surprising that the actinic aspect of the "coherer" problem has received so little attention. Prof. MINCHIN'S cell engenders electromotive force when exposed to light; that is its proper function, and it is intimately associated with the coherer--for it is alive, as the coherer is, to Hertz-waves, and to mechanical and electrical tapping back. Can the coherer be rendered sensitive to light? We suggest that it is highly probable that it can.