78 THE ROYAL SOCIETY OF CANADA 



about 2| inches in diameter, designed to be set in vibration by the 

 sound waves and to communicate these vibrations to one of the faces 

 of the carbon-granule capsule. A couple of dry-batteries giving 

 altogether about 3 volts, and a telephone receiver completed the 

 equipment. When tested out by being immersed in the pond of 

 water in the quarry, this microphone proved to be too insensitive for 

 the purpose of receiving signals from any appreciable distance, hard 

 blows with a crow-bar dealt to the solid rock a few feet from the 

 immersed microphone could only be just heard in the telephone 

 receiver. 



(2) A more sensitive microphone of the same type gave much more 

 satisfactory results. The instrument was of the same kind as that 

 already described except that the copper diaphragm was considerably 

 larger (about 6"), corrugated, and very much more sensitive to 

 vibrations. This instrument was employed with a 30-ohm telephone 

 receiver directly connected with the circuit and also in conjunction 

 with an amplifying arrangement to be described later. When this 

 instrument was employed about 2 in. of ice had formed on the» pool 

 of water in the quarry: a hole was cut in the ice and the microphone 

 was let down into the water at a point where it was about 5 ft. deep. 

 In these circumstances the note of the oscillator could be distinctly 

 heard in the telephone, both when directly connected into the circuit 

 and very much more distinctly when the amplifier was employed. 

 That the transmission was genuinely through the rock and not from 

 the air, through the ice to the water, was ascertained by noting that a 

 short signal from the oscillator could be heard first in the telephone and 

 then directly through the air. These observations indicate that vibra- 

 tions of intensity sufficient to be detected at 100 ft. distance by the means 

 at our disposal could be transmitted through the bed rock by the very 

 imperfect arrangements employed. It thus seems probable that, by 

 employing the more elaborate methods already mentioned, of securing 

 good "acoustic contact" between the oscillator and the bed rock, and 

 by employing more sensitive microphones with the high-ratio amplify- 

 ing devices now available, it should be possible to increase this range 

 of transmission ten or twenty times, depending on the homogeneity 

 of the rock-medium through which the signals are transmitted. 



An attempt was made to receive signals from long distances, 

 employing the microphone just mentioned. A pit about 6 ft. deep 

 was dug through the earth to the bed rock at a point about 230 yards 

 from the oscillator. This hole was filled to a depth of 3 ft. with water 

 in which the microphone was immersed. Reception was tried, both 

 with the telephone directly connected into the circuit and with the 

 amplifier described below. No sound which^ could be attributed 



