76 THE ROYAL SOCIETY OF CANADA 



purpose, as is in fact mentioned by the inventor himself.^ A des- 

 cription of this apparatus, which is now well known, is given in several 

 easily accessible journals.^ It is sufficient to state that by adopting 

 the principle of the rotary induction motor to the production of linear 

 oscillations it has been found possible by the use of very moderate 

 amounts of electric power (2 to 5 K.W.) to generate extremely powerful 

 waves of compression in water, capable of being detected at distances 

 varying from 10 to 30 nautical miles. As rock is, on the average, 

 only about i^ as compressible as water, it is reasonable to expect that 

 rock vibrations of sufficient intensity to be detected at considerable 

 distances from the source should be capable of being generated by 

 this means. It is obvious that, should the transmission of sound 

 through earth and rock to any considerable distance prove to be 

 feasible by this method, a system based on this method might prove 

 to be of considerable practical value in such fields as geological survey 

 work, mine communication, etc. 



Section 3.— Experiments Carried Out at Macdonald College 



Ste. Anne de Belle vue, on the Transmission of Sound 



THROUGH Rock. 



With the possibility of these applications in mind, advantage was 

 taken of having at hand a Fessenden oscillator — employed in some 

 tests on acoustic soundings, by one of us, (L.V.K.), to carry out a 

 few preliminary experiments on the possibility of transmitting sound 

 through solid rock, especially with a view to determining to what 

 extent the standard apparatus employed in undersea work could 

 be adapted to the purpose under consideration. Facilities for carrying 

 out these tests at Macdonald College, were kindly provided by the 

 Principal, Dr. F. C. Harrison. 



Sound Generating Apparatus. 



As bed rock was accessible in a small quarry situated in the 

 College grounds at a short distance from a 220-volt D.C. transmission 

 line from the College power station, it was decided to set up the oscil- 

 lator and the accessory apparatus at this point. A small portable 

 shanty was therefore moved to this neighbourhood and in this was 

 installed the motor-generator set, controlling rheostats, operating 

 keys, etc. The line voltage (220 volts) was reduced to the 110 volts 



'Fessenden, R. A., "Long Distance Submarine Signalling by Dynamo-Electric 

 Machinery," Lecture given to the American Academy of Arts and Sciences, Feb. 

 25th, 1914. Published by the Lawrence Scientific Association, June, 1914. 



^Blake, "Submarine Signalling", Trans. Am. Inst. E.E., Oct. 1914, pp. 1569-1583. 

 Discussion May, 1915, pp. 1046-1049. 



