414 Sounds we cannot Sear. 



I witnessed the experiment of sounding a set of small organ 

 pipes of extreme acuteness of tone. The Professor slowly and 

 regularly opened the air-valve of one pipe after another, 

 beginning with the gravest, the sound of which we all heard, 

 not only distinctly but disagreeably in its shrillness. " What 

 a squeal it is !" whispered a fellow- student to me. " Ah ! 

 now it's quiet, that's a blessing," said he, as a yet more acute 

 pipe was sounded. " Quiet !" I replied, " why, it's twice as 

 bad." "1 can believe my own ears, I imagine," was the 

 rejoinder, " and I know the squealing has ceased." After two 

 or three other pipes of constantly increasing acuteness had 

 been sounded, I whispered to him rather loudly, supposing the 

 experiment to be concluded, "Now, it is really stopped." 

 " Bosh !" muttered a Scotch lad, just by, " If ye canna hear 

 yon skreigh your ears are no that good." 



To the utter amazement of all of us, we found that we could 

 not at all judge of one another's powers of hearing for shrill 

 sounds. Several persons were unable to hear notes which to 

 me were perfectly clear and distinct ; while what appeared to 

 me complete silence, was to others broken by an ear-piercing 

 shriek. 



What appeared most singular was that the power of hearing 

 more or fewer of these acute notes bore no relation to ability 

 to catch slight sounds, or to the loudness of the note 

 sounded.* It was not a matter of more or less distinctness of 

 sound, but absolutely of sound or no sound. A person 

 standing close to the instrument when a note too acute for his 

 hearing capacity was given forth, could no more hear it than 

 if he had been ten miles away, although it might seem to his 

 neighbours but little shriller than the note immediately pre- 

 ceding, which" he had heard as well as they could do ; yet to 

 him this was no sound at all. 



Before the smallest pipe of the tiny organ had been reached, 

 all present had ceased to hear the sounds produced, and we 

 knew, merely from seeing the action of the bellows, or feeling 

 the rush of air through the little tube, that a note was being 

 sounded, although to us totally inaudible. 



From various experiments with the " Siren," it has been 

 shown that the human ear can, under favourable circum- 

 stances of intensity, distinguish as continuous sounds vibrations 

 ranging from fourteen to sixteen in the second of time up to 



* The pitch of a sound depends upon the number of vibrations in a given 

 time. Its intensity depends on the amplitude of the oscillation. Loudness, or 

 intensity, when carried to extremes, was found by Savart to have a material 

 influence in enabling persons to hear sounds to which they were deaf under 

 ordinary circumstances. The statement in the text is true within the usual limits 

 of intensity. — Ed . 



