THE PRODUCTION OF SOUNDS 223 



moreover, picked up sounds which they claim were emitted by Hump- 

 back and other big whales, while a recording of whale noises made at the 

 Biological Station at Woods Hole reproduces an intermittent hum 

 resembling the sound of a ship's screw. This hum, however, may have 

 merely resulted from the animal flailing its tail. 



Other investigators, such as Hosokawa (1950), Schevill and Lawrence 

 (1952) and the British biologist Symons, who did research work aboard 

 the Balaena, were unable to pick up any Rorqual noises, much as they 

 tried to do so. (The only sound Schevill managed to pick up in 1958 was 

 a 'generator hum' emitted by a Biscayan Right Whale.) Even so, it seems 

 unlikely that Rorquals, whose auditory organs are so well adapted to 

 picking up underwater sounds, should be less capable of emitting noises 

 than dolphins. Sperm Whales and Biscayan Right Whales. No doubt, 

 improved equipment and methods of observation will lead to better 

 results in the future. 



In any case, we have seen that dolphins, at least, can produce noises up 

 to 1 70 kilocycles per second and that they respond to sounds of between 

 150 and 153,000 cycles per second (see Chapter 7). This would enable 

 them to distinguish clearly between noises emitted by their own species 

 and the low-pitched sounds offish. 



Such high pitch sounds make us think of bats whose ability to find their 

 way about in complete darkness is known to be associated with the high 

 notes they produce, so much so that, as the well-known eighteenth-century 

 naturalist Spallanzani proved, blinded bats lose none of their sureness of 

 flight. The exact mechanism of their flight had long puzzled biologists, 

 particularly when it appeared that the animals' feelers played no part in 

 it. The problem \vas finally resolved with the discovery of the principle of 

 radar which, as we know, is based on transmitting very short radio waves 

 and receiving them again after they have been reflected by solid objects. 

 Radar is used inter alia by ships sailing in thick fog and in the vicinity of 

 icebergs, and the risk of collision is consequently minimized. 



Now a great many investigators, including Prof. Dijkgraaf of Utrecht, 

 have shown that the remarkable flying feats of bats are based on a similar 

 principle. Bats emit high-frequency sound waves through their mouths 

 and noses, and pick up any reflected signals by ear. In this way, they 

 manage to avoid obstacles in their path without having to use their eyes. 

 Ultrasonic vibrations are particularly suited to this purpose since they can 

 be beamed in a given direction far better than low-frequency vibrations. 

 What we know about bats leads us to assume that whales and dolphins, 

 whose hearing is so extraordinarily acute and whose other sense organs 

 are so poorly developed, and which, after all, spend much of their time 

 groping in the dark of the lower ocean or under the ice, hear and avoid 



