. Discovery. Science. Aerial Fig. I. A tlirce-clcctrode transmitting valve. A is a plate of sheet metal, b is a cylinder of .nar- row mesh wire 'gauze, c is a wire filament. The glass vessel is highly evacuated. FiG. : showed that such an arrangement was not suitable for immediate use. In comparison with wireless telegraphy, the advances in wireless telephonj' were slow until about six years ago, when the Three-Electrode Thermionic Valve was introduced as a generator of wireless waves. Since then, however, such rapid progress has been made that its great future is already well assur
. Discovery. Science. Aerial Fig. I. A tlirce-clcctrode transmitting valve. A is a plate of sheet metal, b is a cylinder of .nar- row mesh wire 'gauze, c is a wire filament. The glass vessel is highly evacuated. FiG. : showed that such an arrangement was not suitable for immediate use. In comparison with wireless telegraphy, the advances in wireless telephonj' were slow until about six years ago, when the Three-Electrode Thermionic Valve was introduced as a generator of wireless waves. Since then, however, such rapid progress has been made that its great future is already well assured. The principal reason why telephony lagged so far behind was that a continuous radiation of uniform ether waves which could be modulated by the voice was essential, whereas in telegraphy a radiation of groups of waves sufficed, a radiation such as was obtained from the spark generators used in all the earlier wireless telegraph transmitters. The first real attempts at wireless telephony were made possible when arc generators and high-frequencv alternators are generated, and when these currents are caused to flow in an aerial, a continuous stream of uniform ether waves is radiated. For telegraphy, these oscillations, and hence the waves, are broken up into short and long groups bj- a signalling ke\-, corresponding to the dots and dashes of the Morse Code ; and for telephony they are modulated by the voice speaking into a microphone, just as the current in the line is modu- lated in line telephony. A common form of micro- phone consists of a small chamber filled with carbon granules through which the current flows, the current remaining constant so long as the granules are quiescent, but varying in strength owing to the varying electrical resistance, as the granules are made to vibrate by the voice. The microphone transmitter may be placed as in Fig. 2 at M in the aerial itself, so as to modulate the. Please note that these images are extracted from scanned page images that ma
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