FIRST EVENING DISCOURSE. 735 
Mr. Marconi in 1905 claimed to have already reached a speed of a hundred words 
per minute by the spark method, and lately there has appeared in the technical 
press examples of high-speed signalling by the British Post Office over a distance 
of 15 miles in which readable signals were received at a speed of seventy words 
per minute. 
Turning to the receiving end, almost all the receivers that have been used in 
the spark method can be equally well used for the are method; for it must be 
remembered that the transmission in either case is affected by Hertzian waves 
traversing space, and that the only fundamental difference consists in the number 
of oscillations in each train of waves. It must be noted, however, that in those 
methods in which a telephone receiver is used it is necessary to break up the 
continuous oscillations of the are method into groups succeeding one another 
sufficiently rapidly to produce an audible sound in the receiver; for in the spark 
method the sounds we hear in the receiver correspond with the succession of impulses 
of the diagram, one for each spark at the transmitter. This chopping up of the 
continuous wave-train so as to produce audible signals in the receiving apparatus 
can be done either at the transmitting end or in the receiving apparatus. An 
example of this latter method is Poulsen’s ticker. 
The question whether receiving apparatus can be arranged so as to receive 
messages from stations equipped with the spark apparatus and from stations 
equipped with the are apparatus is a matter of enormous importance at the 
present moment in view of the probable ratification of the Berlin Convention, 
which imposes an obligation on all commercial stations to intercommunicate 
without regard to the make or system of transmitting apparatus employed. I am 
of the opinion that there will be no difficulty in carrying this into effect provided 
that the stations using the spark method send out long trains of waves, as they 
should do to obtain syntonic working, which is also called for by the Berlin 
Convention. 
An extremely interesting development which is now progressing rapidly, owing 
to the possibility of producing continuous oscillations by the arc method, is wireless 
telephony. Suppose that we can vary the intensity of the oscillations in a manner 
corresponding with the vibrations of the air which constitutes sound and speech, 
then we should obtain at the receiving stations a train of Hertzian waves whose 
amplitude varies in a corresponding way; by allowing these waves to act ona 
telephonic receiver which is sensitive to the intensity of the waves we shall 
obtain in the telephone a reproduction of the sounds. This has actually been 
carried into effect by employing an ordinary microphone to modify the current 
through the transmitting arc so as to vary the intensity of the oscillation current 
produced, and by employing what is known as a point-detector and a telephone 
at the receiving station. 
Another method which may be used consists in causing the microphone to 
vary the frequency of the oscillations of the generator, and by arranging the 
receiver so that it is more or less strongly affected according to the frequency of 
the received waves. 
I am informed that such good results have already been obtained on the 
experimental stations for wireless telephony that it is proposed to equip stations 
at Oxford and Cambridge for the further perfecting of this application. 
It is greatly to be desired that wireless telephony may develop rapidly, as it 
seems to me that for the purpose of communicating with ships wireless telephony 
will have great advantages over wireless telegraphy. 
I am deeply indebted to Mr. Colson for all the facilities that he has placed at 
my disposal, and to his engineers for their assistauce, which has enabled me to 
carry out the experiments in the lecture ; and I have also to thank the Tramway 
Department for the special supply of current. 
