1907.] on Recent Contributions to Electric Wave Telegraphy. 699 



instruineut was shown by me to the Royal Society early in February 

 19(»5, and was employed by Mr. Marconi soon after as a long-distance 

 wireless-telegraph receiver, in conjunction with other improvements. 

 M. Tissot, of tlie Naval College, Brest, in France, has made use of 

 this glow-lamp detector, and with a sensitive galvanometer has re- 

 ceived signals at a distance of 50 kilometres.*' Employing a special 

 form of transformer, and a telephone in place of a galvanometer, 

 Mr. Marconi has used it for some time past over distances of 

 200 miles or more, and finds it a very sensitive form of receiver. 

 Since this particular form of electric wave detector was Ijrought to 

 notice by me. Dr. Wehnelt has found that a metallic wire, coated 

 with oxides of calcium, barium, or other earthy metals, may be sub- 

 stituted for the carbon filament in the vacuous bulb. 



The oscillation valve is capable of giving very remarkal^le effects 

 when used as a receiver with a transmitter producing undamped 

 waves. The reason for this is obvious. The valve passes all the 

 unidirectional currents in the attached secondary circuit. If, then, 

 these are intermittent damped trains, say having a frequency of 

 100,000, and 50 trains of 20 oscillations per second, the total time 

 during which electric cun-ent is passing is only one-thousandth of 

 the whole time. Accordingly, if we, so to speak, fill up the gaps 

 between the trains of oscillations with other oscillations, and generate 

 a continuous train, we greatly increase the quantity of electricity 

 passing and re-passing any point in the secondary circuit, and the 

 indications on a galvanometer in circuit with the valve are enormously 

 increased. A true comparison between the two cases of damped 

 and undamped waves involves many factors, and is not fair unless 

 we compare together transmitters taking the same mean power. 

 Generally speaking, however, we may say that not only this glow- 

 lamp detector, but all forms of thermal detector, give greatly 

 increased effects when employing undamped oscillations. I find, 

 for instance, that if undamped oscillations are created in a closed 

 wire circuit which forms part of a circuit containing capacity and 

 inductance shunted across a Poulsen arc, I can induce powerful 

 secondary oscillations in a similar closed and syntonic secondary 

 circuit at a considerable distance, and detect these by the use of my 

 oscillation valve and a galvanometer placed. In fact the use of 

 undamped oscillations in a closed primary circuit, and this oscillation 

 valve used with a telephone in a closed secondary circuit, brings to 

 the front again the possibility of making use of so-called wireless 

 telegraphy by electro-magnetic induction over very large distances. 

 The old form of electro-magnetic induction telegraphy as practised by 

 Trowbridge, Preece, Lodge and others made use of low-frequency 

 alternating currents (50 to 100) in a closed primary circuit, and 



* See The Electrician, vol. Iviii., p. 730, Feb. 22, 1907. M. C. Tissot, "On 

 Ionised Gas Electric Wave Detectors." 



