490 



NATURE 



[June i6, 192 i 



at large, I do not believe he is averse from employing 

 crucial tests. His difficulty in the manifold processes 

 of life is to formulate tests that really are crucial. 

 Sir Archdall Reid thinks it an easy matter, and he 

 takes recapitulation as an instance. At the moment 

 when his letter was published some of us were dis- 

 cussing that very question at the Linnean Society, and 

 Sir Archdall Reid, had he been present, would have 

 seen that the issue was far from being the simple one 

 that he imagines. F. A. Bather. 



June 4. 



A New Acoustical Phenomenon. 



When living near Croydon aerodrome during the 

 earlier part of the war, I noticed that the higher- 

 pitched sounds apparently given out from an aeroplane 

 flying nearly overhead varied with the height of my 

 ear above the ground ; thus, by bending down to one- 

 half one's normal height, the pitch of this higher note 

 rose an octave. I have on many recent occasions 

 confirmed this result. This phenomenon Is most 

 noticeable when standing on a smooth road or lawn, 

 and is scarcely distinguishable on a rougher surface, 

 such as a hayfield; the logical conclusion is therefore 

 that it is due in some manner to reflection from the 

 ground. The pitch of the note varies also with the 

 angle of elevation of the aeroplane,' and Is not generally 

 audible unless this is more than about 45 . Since 

 the pitch rises continuously as the head is lowered, 

 the apparent explanation Is that the note is due to the 

 Interval between the arrival of the direct and reflected 

 waves from impulses radiated from the aeroplane — that 

 is to say, no note of this definite pitch comes through 

 the air from the aeroplane, only a regular, or 

 irregular, succession of impulses, the time periods of 

 which have no relation to the observed note, for it is 

 obvious that merely bowing to the aeroplane could not 

 alter the pitch of any note it might be giving out. (It 

 is well known that a note of much lower pitch, due 

 to the engine, is always present, but it is not in this 

 sound that the variation takes place, although it is 

 possible that these are the waves from which the 

 variable high note Is produced by reflection.) The 

 pitch of the sound with which we are concerned is 

 thus due to the fixed interval between the arrival of 

 the direct and reflected Impulses, and thusi depends 

 upon the height of the observer and the angle of 

 elevation of the aeroplane. An interesting deduction 

 from the discovery Is that the ear Is able to appre- 

 ciate pitch from a succession of double impulses, if 

 the interval between the elements of each double 

 impulse Is constant. 



The phenomenon Is not in any way peculiar to 

 aeroplane noises ; I have observed it with equal dis- 

 tinctness, though the sound was fainter, when stand- 

 ing under an aspen tree In a light breeze. Through 

 the rustle of the leaves could be distinguished a note 

 of quite definite pitch, which, as before, rose to its 

 octave on lowering the head to half one's height. 



In support of the explanation I have given, it may 

 be remarked that the pitch of the note observed seems 

 to correspond with the interval of time between the 

 arrival at the ear of the direct and reflected impulses 

 as calculated from the velocity of sound in air. 



From the physiological p>oint of view it would be 

 interesting to make a laboratory test, using a disc 

 siren with the holes pierced In groups of two, all 

 pairs being similar to one another, but grouped at 

 unequal spaces on the circumference ; thus the passage 

 of each pair would give a double puff, but the double 

 puffs would be in an irregular succession. This 

 would, no doubt, give a definite note corresponding 

 in pitch to the interval between members of a pair of 

 NO. 2694, VOL. 107] 



holes, and would be a further confirmation of my 

 explanation. 



That two impulses alone appear to give a sense of 

 definite pitch Is Interesting, and seems to Indicate the 

 existence of a resonating system In the ear. Experi- 

 ments such as I have suggested, with a disc siren, 

 might therefore help In the solution of the much- 

 discussed problem of the function of Corti's organ. 

 Another and more general series of experiments would 

 have the object of finding whether, as is Indicated 1d\" 

 my observations, all sounds when heard by an ob- 

 server near a reflecting surface have, in addition to 

 the incoming fundamental note, a note of a pitch 

 depending on the distance of the observer from the 

 reflector. This phenomenon Is known to have 

 occurred, as regards electric waves, in Hertz's 

 classical experiments. Unfortunately press of other 

 research work prevents me from carrying out tests 

 In this fascinating subject, but perhaps someone more 

 directly interested may find time to develop It further. 



J. Erskine-Murray. 

 Directorate of Research, 

 .\Ir Ministry, Kingsway, London, W.C.2. 

 June 7. 



Herons and Fish. 



It was commonly believed and asserted by old-time 

 writers on natural history that from the feet and legs 

 of the common heron exuded an oil with a peculiar 

 odour which attracted fish within striking distance of 

 the bird's powerful beak. Anglers used to mix the 

 fat of a heron with flour and other matter and anoint 

 their baits with it, whereby, says John Jonston in 

 his " Historia Naturalls " (1657), "mirifice pIsces 

 illiciuntur." 



I have never regarded this theory as of greater value 

 than many others propounded by medieval empirics, 

 but it was recently brought vividly to mind by what 

 has taken place in the garden of one of my country 

 neighbours. In this garden there is a rectangular 

 pond measuring about 30 ft. by 20 ft. The sides are 

 of dressed masonry, which extends under 9 in. of 

 vi'ater so as to form a continuous ledge a yard broad, 

 beyond which the depth drops suddenly to between 

 3-4 ft., wherein some of Marliac's water-lilies are 

 grown. The pond was stocked with goldfish, which 

 throve well until a heron found its way there, and 

 has succeeded in exterminating them. The owner of 

 the garden, a good observer upon whose statement 1 

 can rely, tells me that the bird always took Its stand 

 in one corner of the pond, on the ledge covered by 

 the shallow water, and that the goldfish moved out 

 of the deep water into the centre and congregated 

 round the heron, who picked them up at leisure. Had 

 the fish remained in the deep water which they usually 

 Inhabited, of course the heron could not have reached 

 them. 



Although I draw no inference from this incident, it 

 seems worth mentioning. It would be interesting to 

 hear of an authentic parallel case. 



Herbert Maxwell. 



Monreith, Wigtownshire. 



Why do Worms Die? 



Many times during the last twenty years I have 

 been tempted to make the following communication. 

 My house backs on to, and is partly built into, the 

 old cliff at St. Leonards-on-Sea, and my back door 

 opens on to a road cut into the face of the cliff. The 

 road is well tar-macadamed and watertight. The 

 esplanade at St. Leonards Is wide, tar-gritted, and 



