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THE ROYAL SOCIETY OF CANADA 



reception of vibrations transmitted through rock unless special means 

 of amplification are employed, owing to the extremely small amplitude 

 of vibrations set up in the carbon-granule capsule. If the principle 

 of the contact microphone is to be employed, means should be taken 

 to magnify the amplitude at the contact as much as possible; in the 

 case of detecting rock-vibrations the rigidity of the vibrating medium 

 enables this to be done, as in this case for the same amount of power 

 transmitted, a much larger amount of energy is available for operating 

 a mechanical system of amplification. With this principle in view, 

 a mechanical leverage similar to that employed in the gramophone 

 sound-box was fitted to an ordinary Blake "solid-back" carbon 

 microphone telephone transmitter as shown in Fig. 1 . 



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Figure 1 



The transmitter was mounted on elastic supports in the manner of 

 a miniature seismograph so as to respond to vertical and horizontal 

 components of vibration. Experiments with this type of design 

 gave very promising results: although the diaphragm of the trans- 

 mitter was removed, the instrument proved to be very sensitive to 

 sound-waves. On one occasion it was thought that signals through 

 bed rock had been transmitted over a distance of 230 yards: closer 

 investigation revealed, however, that although the sound vibrations 



