1909] on Researches in Radiotelegraphy. 681 



strong transverse magnetic field and also in a hydrocarbon gas, as 

 shown by Ponlsen, or we may employ a number of arcs in series. 

 E. Ruhmer has lately also employed a high tension arc between 

 aluminium electrodes (see Fig. 21), shunted by a condenser and in- 

 ductance as a means of generating persistent oscillations. As an 

 alternative, it is possible to create them by a mechanical method, 

 viz. l)y a high frequency alternator, subject, however, to certain 

 limitations as to frequency. Both these types of generator have 

 their advantages and practical objections. There is good evidence 

 that radiotelephony has been accomplished over distances of 100 miles 

 or more by each of these methods in the hands of experts, but what 

 is now required is the reduction of the apparatus to such simple 

 manageable and practical form that it can be applied in regular work. 

 The wave-generating apparatus must be capable of producing uniform 

 persistent oscillations of high voltage and frequency, not less than 

 :30,000 or 4(1,000 per second, or at least above the limits of audition, 

 and the amplitude of these oscillations must be capable of being- 

 varied by some form of speaking microphone placed in the oscillation 

 circuit or in the radiating antenna, or in a secondary circuit coupled 

 to it. No ordinary simple carbon microphone will safely pass suffi- 

 cient current for this purpose. A type of multiple microphone has 

 been used successfully and also a duplex microphone, the invention 

 of Ernst Ruhmer. 



It is not, however, possible to speak of radiotelephony at the 

 present time as having reached the same level of practical perfection 

 as radiotelegraphy. But the possibilities of it are of such a nature 

 that it will continue to attract the serious attention of inventors. 

 This is not the place to enter into a full discussion of the causes 

 which limit suljmarine telephony through cables, but there are well- 

 known reasons in the nature of submarine cables as at present made 

 which impose very definite limits upon it, owing to what is called 

 distortion of the wave form. Electric wave telephony is free at least 

 from this disadvantage, and if (as has been asserted) arc generators 

 can be made self -regulating and capable of being worked for hours 

 automatically, or even for 10 minutes without being touched, then 

 the remaining difficulties with the microphone are not insuperable. 



Time does not permit of the discussion of the many other points 

 in connection with radiotelegraphy and telephony which have been 

 the subject of recent work. Much attention has been paid lately to 

 methods of cutting out atmospheric signals due to natural electrical 

 discharges in the atmosphere, which are troublesome disturbers of 

 the aBtherial calm necessary for radiotelegraphy. Considerable 

 thought and expenditure have been necessary to discover means for 

 overcoming the difficulties of long distance transmission by daylight, 

 and also those arising from the cross talk of other stations. Much 

 also has been done in training skilled wireless operators both in the 

 Navy and for the mercantile marine work. Radiotelegraphy, like 



2 Y 2 



