Recent advances in wireless telegraphy
Journal of the Institution of Electrical Engineers
In the earlier part of the paper the chief systems in use were shortly described, and their-methods of action discussed. Methods of discrimination between stations by the use of equifrequent electrical vibrators at the transmitting and receiving ends were explained, and instances given, the most striking example being that reported by Captain Jackson, R.N., the exact details of which are as follows: The Vernon received signals from Poldhu, 180 miles distant, on one mast, and at the same time
... at the same time sent signals to a ship 50 miles away by a separate aerial on another mast about 200 ft. from the first. The receiving was quite unaffected by the sending. Various forms of responders or detectors were then described, and mention was made of some recently patented systems which have not yet come into commercial use. The Action of the Coherer.-The coherence of metal filings or surfaces was supposed at first to be due to electrical oscillations, and to be a test for their presence. I have never held the view that oscillations were necessary, believing that all that is required is merely an electrostatic field or difference of potential which causes the particles to join up in chains as do iron particles in a magnetic field. That small particles do so in an electrostatic field has been shown by Robertson and others. When the ends of the particles come within a very small distance of one another a spark passes even if the voltage be low, and the welding takes place. The action is facilitated by very gentle intermittent mechanical shocks (tapping) just as in the case of iron filings in a magnetic field. Severe shaking, of course, prevents any chains from forming, or breaks up such as have been formed. The action of a filings coherer thus takes place in two stages-first, the movements of the particles, and second, the welding. That this view is correct has been amply proved by Dr. W. H. Eccles in an able experimental research which he undertook at my suggestion. He has also deduced a mathematical theory of the action which fits the results of experiment, and invented a method for testing coherers in the laboratory without the use of telegraphic apparatus.