DISCOVERY 



straight lines, quarters by a small " v." The highest 

 number recorded is 19,000. 



Although it is true, as already stated, that scholars 

 still await a clear starting-point for transcribing the 

 Cretan script, there is one interesting and important 

 point already established by Sir Arthur E\'ans. He 

 has proved that the Phoenician alphabet, which had 

 always been supposed to be the original source of the 

 Greek alphabet, and therefore of the Latin alphabet 

 from which comes our own, was itself derived from 

 Crete . 



There are in existence three fragmentary inscrip- 

 tions, two of which were found not long ago by Pro- 

 fessor R. C. Bosanquet at Pra;sos, in Crete — near to 

 Mount Dicte, and not far to the north-east of the boun- 

 daries of Knossos — which are written in Greek charac- 

 ters, and are therefore quite legible to us, but which 

 contain a language which is not Greek. Is it the 

 language of the Minoans ? On this thorny question I 

 must leave it to Professor Conway, who has examined 

 them at length in the Annual of the British School at 

 Athens,' to find what can be said — if anything can be 

 — to the readers of Discovery. 



• Vol. viii, p. 125, and vol. x, p. 115 



(To be concluded) 



Wireless Telephony 



By Lieut.-Gol. C. G. Crawley, M.I.E.E. 



In communicating by speech in the ordinary way, 

 energy is transferred from the speaker to the listener 

 in the form of air waves, these waves being produced 

 by oscillations, to and fro, of the little particles of air 

 These air oscillations are set up by the voice, and are 

 received as air oscillations in the ear, where the}" set 

 the drum in vibration, so producing the sensation of 

 sound. In line telephony the air oscillations set up 

 by the voice actuate an instrument, the microphone 

 transmitter, which varies the strength of the electric 

 current flowing along the line. These variations of 

 the current work the receiving instrument, the tele- 

 phone receiver, in such a way as to produce sound 

 waves precisely similar to those which caused the 

 variations at the sending end. In this way the energy 

 of the air oscillations at the transmitter is transformed 

 into the energy of current variations in the line, and 

 retransformed into sound at the receiver. 



In the case of wireless telephony the procedure is 

 very similar, except that the variations of a current 

 flowing in a s\'stem of elevated wires, called the aerial 

 or antenna, produce variations in the continuous 

 stream of ether waves which this 'current causes to be 

 radiated in all directions, and these ether waves cause 



a current with similar variations to flow in any other 

 aerial which they meet. 



In ordinary speech, therefore, air waves proceed 

 direct from the sender to the receiver ; in line tele- 

 phony they vary an electric current which produces 

 similar air waves at the receiver ; and in wireless 

 telephony they vary an electric current which pro- 

 duces variations in ether waves, which in their turn 

 produce similar air waves at the receiver. 



The medium by which energy is transferred in line 

 telephony is the wire connecting the sender to the 

 receiver, whereas in wireless telephony the medium 

 is the ether which connects all senders to all receivers, 

 and it is this fact which constitutes the great advan- 

 tage of the latter, viz. all senders are at no cost auto- 

 maticallj' connected to all receivers. It must not be 

 thought, however, that such a great advantage can 

 be attained without dragging some serious disad- 

 vantages in its train. The use of the same medium, 

 for instance, leads naturally to difficulties in selec- 

 tivity — that is, one communication being interfered 

 with by others, or by electrical disturbances in the 

 ether itself, such as those caused by lightning. Inter- 

 ference between various communications is overcome 

 to a great extent bj' arranging that different lengths 

 of waves in the ether are used for different communi- 

 cations, the apparatus for one communication being 

 adjusted to respond much better to ether waves of 

 one special length than to those of any other. When 

 the apparatus at each end are thus arranged for 

 transmitting and receiving respectively ether oscilla- 

 tions of the same rate, they are said to be in tune 

 with one another, and the greater the number of 

 different communications required, the greater are the 

 number of various rates of oscillation that must be 

 arranged for. Now, it is just this requirement that 

 makes an extensive network of different communica- 

 tions very difiicult and often impracticable, because 

 for good working over approximately the same range, 

 the various wave lengths that can be economically 

 used are strictly limited. Wireless telegraphy makes 

 use also of ether waves, and requires the same wave 

 lengths as are suitable for telephony, so that the 

 available field for selection is still further reduced. 

 With line telephony, on the other hand, there is of 

 course no such limitation, separate wires being used 

 for each of the various communications. 



The other trouble mentioned, that of interference 

 from electrical disturbances in the ether, is also very 

 serious, just as it is in the case of wireless telegraphy. 

 These disturbances, or " atmospherics," are very 

 troublesome indeed in tropical climates, and even in 

 temperate latitudes they produce much interference 

 in the summer months. For "broadcasting" a 

 message — that is, sending a message out to all stations 



