[boyle] cavitation 161 



The point raised in this paper should be tested experimentally 

 for final settlement, but unfortunately we have no practical cases 

 where the emission of energy is great enough for this phenomenon of 

 cavitation to intervene. 



In air, King^ has measured approximately the energy emission 

 from a modern diaphone used as a fog-alarm, and found at the greatest 

 emission, under the best conditions, an energy flux of 2.36 H.P. for 

 14 sq. inches of surface in the trumpet of the instrument. This is a 

 rate of only 19.5 watt per sq. cm., which is much too small for any 

 test of the kind required here. 



Fessenden^ has asserted concerning the Fessenden submarine 

 oscillator that operating at a frequency of 500 '-^/sec. there would be 

 no difficulty by suitable design in obtaining 35 H.P. delivered to the 

 water. If the diaphragm of such an instrument had a radiating 

 surface of twenty inches diameter, as in the case of the ordinary 

 Fessenden oscillator, this emission of energy would correspond to a 

 rate of 17.3 watts per sq. cm. As shown by the tabulated figures 

 above this would be about ten times the rate of energy propagation 

 required to test the question of cavitation, but no such energy emis- 

 sions in water have been accomplished practically. In some cases of 

 the use of a Fessenden oscillator the sound energies emitted in the 

 water were found to be about 350 watts at a frequency of 300 '^/sec, 

 and 500 watts at a frequency of 540 '^/sec. For a twenty-inch 

 diameter diaphragm these emissions correspond to rates of 0.017 and 

 0.025 watts per sq. cm., respectively. The figures tabulated above 

 show that rates fifty times greater would be required to test for 

 cavitation as here described. 



The writer has recently experimented with an energy emission of 

 about 0.09 watts per sq. cm. of radiator surface, but this rate of 

 emission would have to be increased five times before any hope of 

 testing this cavitation experimentally could be entertained. 



The above figures of practical sound production illustrate how 

 difficult it is to transform large amounts of energy into actual sound 

 waves, and that all apparatus for sound production must be "ineffi- 

 cient" in the scientific sense. 



^Acoustic Efficiency of Fog-Signal Machinery, Phil. Trans. A, Vol. 218, pages 

 211-293. 



^Fessenden, Long-Distance Submarine Signalling, Lawrence Scientific Ass., 

 June, 1914, p. 15. 



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