176 



iProfessor J. A, Fleming 



[May 21, 



The discovery of the oscillation-producing power of the valve 

 was of great importance, because it at once put it in our power to 

 conduct wireless telephony with simple easily-managed apparatus. 

 The principles of radio-telephony are briefly as follows : At the 

 transmitting station we have to establish in the sending aerial 

 undamped or persistent oscillations, and to radiate continuous waves. 

 This corresponds to a lighthouse which is emitting a steady persistent 

 beam of light. By means of a carbon microphone we have then to 

 modulate the amplitude or intensity of these waves in accordance 

 with the wave form of the speaking voice. Any articulate sound we 

 can utter is built up of syllables, each of which generally comprises a 

 certain vowel-sound with a more or less abrupt beginning or ending 

 due to the consonant. The vowel sound is a series of sound-waves 



Y/i.vt form of i Scund. 



wvwwwv 



Un£*mf>ed Of C til At cons 



l/a-riiKims of dm}ltli>aLt oj oso.Ualt.oni 



in itcorisn'f w-ilk un-e form 



Fig. 12. — Vaeiation of Amplitude of Continuous Waves in 

 accordance with speech wave form. 



which at any point through which they pass create compressions or 

 rarefactions in the air, and the mode in which these states vary with 

 time may be represented by the ordinates of a curve called the wave 

 form curve, the abscissa? denoting the corresponding time. 



These sound-waves acting on the diaphragm of a carbon micro- 

 phone transmitter are caused to produce similar variations in the 

 electric current flowing through it. 



The arrangements for a wireless telephone transmitter are, then, 

 as follows : By means of a thermionic valve, with its plate and grid 

 circuit inductively coupled, we set up, as already explained, persistent 

 electric oscillations in the plate circuit, and these are transferred by 

 induction to an aerial wire properly tuned to sympathetic vibration. 

 High frequency electric currents therefore flow up and down the 

 aerial. These produce magnetic and electric effects in surrounding 



