ACOUSTIC TELEGRAPHY . 
3 
The call is formed, for the transmitting station at least, by an 
opening made in the diaphragm, behind which is placed a 
harmonium reed. To set it in motion, a speaking tube is 
fitted to the mouth of the apparatus, and when this tube is 
blown into, the reed is thrown into vibrations which, being 
directly communicated to the diaphragm of the telephone, 
make it produce induced currents sufficiently powerful to 
cause the receiving apparatus to emit a comparatively loud 
sound like that of a horn. To transmit speech it is only 
Fig. 8. 
necessary to speak in front of the mouth of the acoustic tube 
as in the ordinary system. 
The apparatus may, however, be so arranged as either to 
reproduce speech in a loud voice, or merely in a low voice as 
in the ordinary systems. When it is required to speak loudly, 
the mouth of the receiving apparatus must be provided with a 
speaking trumpet, as in Edison’s phonograph, and the trans¬ 
mitter must be spoken into by applying the mouth to the 
opening of the speaking tube ; the words being pronounced of 
course in a very loud voice. 
When the apparatus is to be used as an ordinary telephone, 
the speaking trumpet of the receiver is replaced by an acoustic 
tube which is applied to the ear; the words pronounced in a 
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