Sound waves travel in air at a speed of 1^087 feet per second 

 (0* C»; 76 cm, pressure) and in water at U, 89O feet per second varying 

 with temperature and pressure. The greater elastic constant of water 

 makes it nearly ideal for the transmission of sound waves. The same 

 hypotheses and laws that apply to sound in the air are applicable to 

 subaqueous sound. 



Audible sound frequencies range from I6 to 20^000 cycles per 

 second. However, the upper limit may be raised with sufficient power. 

 The term subsonic or subaudible sound refers to that part of the sound 

 range below I6 cycles per secondo Ultra or supersonic refers to the 

 inaudible frequencies extending above 20^000 cycles per second. 2/ Some 

 generators now in use are capable of producing inaudible ultrasound of 

 12^000^000 cycles per second. Recently this part of the sonic band has 

 been developed to homogenize milkj mix oils and precipitate smoke 

 particles. The high frequency sirens have also been used to kill bac- 

 teriaj fish, froges, and other small organisms , They are effective only 

 at extremely short range (50-60 mirio) with almost no "spread" and require 

 tremendous operating power. These machines are for aerial use only, 

 the organisms being held in containers directly in the sound blast. As 

 yet no underwater "death ray" has been produced because of the difficulty 

 of transducing energy into the water. 



To the average fisherj'' biologist, the difficulties of experimenting 

 with sound waves seem almost insurmountable ^ Efficient, continuous, 

 sound wave production lies almost entirely within the realm of elec- 

 tronic warfare. The equipment used to produce controlled sound is for 

 the most part comprised of complex power amplifiers and underwater 

 speakers containing electromagnetic, magnetostriction, or crystal 

 oscillators. This is not a contradiction of the definition of sound 

 given earlier„ In devices of this type, the amplifier develops the 

 power to operate a signal generator which in turn sends electronic 

 impulses to the mechanical oscillatorj, or diaphragm. The vibrating 

 diaphragm imparts sound waves by alternately compressing and rarefying 

 the water. Electronic hydrophones measure the sound field by reversing 

 this system^ 



There are however, simple mechanical means of making imderwater 

 sounds. One of the most productive is the turbine driven with water 

 and air. There are many types of •underwater bells _, clappers, organ 

 pipes, whistles and sirens. It is possible to release air and steam 

 to cause noise in the water, and finally, there are explosives. Fish- 

 ery investigators have experimented with nearly all of these types to 

 obtain response in several kinds of fishes. Most of the investiga- 

 tors were unaware of the need for knowing how much sound energy they 

 were creating in the water, Moorhouse (1932) used a tapper, a buzzer, 

 a bell and a motor horn inside a rectangular can at one end of an aquar- 

 ium. He found that the nervous system of the perch is quite capable 



2j The term supersonic is now used to apply to airplane and rocket 

 flight above the speed of soimd. 



