62 SECTION PHYSICS. 



the tube in order that the calculations should give a correct result. 

 A short whistle with a diameter exceeding two-thirds of its length, 

 will certainly not give a note whose shrillness is governed wholly by its 

 shortness. Therefore in some of my experiments I was driven to use 

 very fine tubes indeed, not wider than those little glass tubes that 

 hold the smallest leads for Mordan's pencils. It occurred to me, in 

 order to produce a note that should be both shrill and powerful, and 

 so correspond to a battery of small whistles, that a simple plan would 

 be to take a piece of brass tube and flatten it, and pass another sheet 

 of brass up it, and thus form a whistle the whole width of the sheet, 

 but of very small diameter from front to back. I have such a whistle 

 here, it makes a powerful note, but not a very pure one. I also made 

 an annular whistle by means of three cylinders, one sliding within the 

 other two, and graduated as before. I find that when the limits of 

 audibility are approached, the sound becomes much fainter, and when 

 that limit is reached, the sound usually gives place to a peculiar 

 sensation, which is not sound but more like dizziness, and which some 

 persons experience to a high degree. I am afraid it is of little use 

 attempting to make the audience hear these small instruments ; but I 

 will try, beginning by making rather a low note. It was found that 

 there was great variability in the audience, in their powers of hearing 

 high notes, some few persons who were in no way deaf in the ordinary 

 meaning of the word, being wholly insensible to shrill sounds that 

 were piercingly heard by others. I find that young people hear 

 shriller sounds than older people, and I am told there is a proverb in 

 Dorsetshire, that no agricultural labourer who is more than forty 

 years old, can hear a bat squeak. The power of hearing shrill 

 notes has nothing to do with sharpness of hearing, any more than 

 a wide range of the key-board of a piano has to do with the good- 

 ness of the sound of the individual strings. We all have our limits, 

 and that limit may be quickly found in every case. The facility of 

 hearing shrill sounds depends in some degree on the position of the 

 whistle, for it is highest when the whistle is held exactly opposite the 

 opening of the ear. Any roughness of the lining of the auditory canal 

 appears to have a marked effect in checking rapid vibrations of the ear. 

 For my part, I feel this in a marked degree, and I have long noted 

 the effects in respect to the buzz of a mosquito. I do not hear the 



