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SCIENCE PROGRESS 



of sound, the speaker, being far away from the wide end of 

 the cone. The inefficiency is due to the fact that the area of 

 the reflecting surface is too small a fraction of the " effective " 

 area appropriate to the long waves employed in speech. It is 



Fig. i. 



as if one were to endeavour to reflect waves on the sea by holding 

 a small flat surface like a spade for them to impinge against. 



If one realises that the long waves of sound are diffusely 

 reflected, and not reflected in accordance with the law of 

 equality of the angles of incidence and reflection, one will 

 understand the uselessness of all instruments that pretend to 



Fig. 2. 



" focus " the sound waves to a point and then convey them by 

 a tube to the observers' ear. See fig. 2. 



In Class C, usually known as trumpets, and illustrated in 

 general design by fig. 3, reflection, ineffective as it must neces- 

 sarily be because of the smallness of the whole reflecting surface, 

 is reduced to nil ; and what little efficiency they possess can 



Fig. 3. 



only be due to resonance. Now if one were to reverse the 

 action of the instrument, and, unscrewing the nipple end, use 

 the instrument with a suitable mouthpiece as a producer of 

 sound, e.g. as a bugle, it would be realised that there is a very 

 limited series of tones that it will emit ; and similarly there 

 is a very limited series of tones to which it will respond. The 



