3 68 PROGRESS OF "WIRELESS" 



in Massachusetts, and also long distance stations in Italy near Pisa and in South America. 

 The scientific explanation of this long distance radiotelegraphy is even now imperfect. 

 It is tolerably certain that if the earth were a metallic sphere and destitute of any atmos- 

 phere long distance wireless telegraphy on it would not be possible. Mr. Marconi not 

 only sends electric waves across the Atlantic but has received signals in South America 

 from his station in Ireland, a distance of 6,000 miles. The problem then is to explain 

 how these electric waves travel one quarter of the way round the earth. The waves 

 used in such work are from 2 to 4 miles in wave length and can undoubtedly bend or be 

 diffracted like light rays to some extent round obstacles. The researches of several 

 mathematicians such as Lord Rayleigh, M. Henri Poincare, Prof. Macdonald and Dr. 

 Nicholson, have, however, shown that diffraction alone will not account for such long 

 distance radiotelegraphy. One attempt to explain it has been advanced by Prof. A. 

 Sommerfeld. He has shown that in the case of a Hertzian oscillator placed at the boun- 

 dary of two medii of different dielectric constant and conductivity, such as the earth and 

 the air, there are surface electric waves which follow round the surface irrespective of 

 curvature. Another theory is put forward by Dr. Eccles. He has given reasons for 

 believing that in a medium such as the upper atmosphere, which is in a state of ionisa- 

 tion due no doubt to the absorption of ultra violet light from sunlight, a long electric 

 wave travels faster than in ordinary un-ionised air. Hence his view is that the upper 

 portion of the wave front advances faster than the lower when radiation takes place 

 from an ordinary vertical antenna. The electric ray may therefore bend to some extent 

 round the curvature of the earth. 



Another question of great importance is the reason for the longer distances which 

 can be covered by radiotelegraphic communication at night than in the day with certain 

 wave lengths. This is in some way connected with the greater ionisation of the air by 

 sunlight during the day. It can be shown that it is not due to mere conductivity im- 

 parted to the air by the ionisation, at least unless this is far greater at high levels than at 

 any altitude at which it has yet been measured. It is probably due to the deflection 

 either upwards or downwards of the electric radiation in virtue of the difference in the 

 velocity of the wave at various levels in the atmosphere. For the waves as used for 

 inter-ship and shore communication the range is about 3 times greater by night than by 

 day, but by the use of a longer wave this difference can be reduced. There are also 

 curious differences in the greater facility of transmission North-South than East- West. 



Another matter to which much attention has been paid is the invention of high 

 frequency generators for the production of undamped oscillations especially required for 

 the achievement of wireless telephony. The inventions of Goldschmidt for multiplying 

 up frequency by the use of a polyphase alternator are important. Duddell and Fessen- 

 den have also devised high frequency alternators. 



The problem of wireless telephony requires not only means for producing persistent 

 trains of electric waves but a microphone or means for modulating them in accordance 

 with the wave form of the speaking voice. Such large current microphones have been 

 devised by Q. Majorana, W. Dubilier, E. Ruhmer and V. Poulsen, and by their aid 

 speech has been transmitted for two or three hundred miles without wires. R. A. Fes- 

 senden has transmitted speech in this manner from Brant Rock to New York City, 

 U.S.A., 200 miles; Poulsen from Lyngby to Esbjerg in Denmark, 200 miles; Lieuts. Colin 

 and Jeance and M. Mercier from Paris to Finisterre, 300 miles; Majorana from Monte 

 Mario to Porto Danzig in Italy. More recently speech has been transmitted radio- 

 tclephonically between Monte Mario and a wireless station on Maddalena Island, 160 

 miles. The apparatus for conducting it generally involves a Poulsen arc generator or 

 some modification for producing undamped electric oscillations. It has not yet been 

 adopted to work as a practical method of intercommunication like wireless telegraphy by 

 ordinary operators. The invention of a simple efficient high frequency alternator 

 producing electric oscillations or some equivalent device is a necessary preliminary 

 to the establishment of wireless telephony on a commercial basis. 



A reversion to the older system of magnetic induction telegraphy has been lately 



