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[Footnote 28: Mr. Hawksley, surgical instrument maker 307 Oxford
Street also makes these.]

The largest whistles suitable for experiments on the human ear, have
an inner tube of about 0.16 inches in diameter, which is equal to 40
units of the scale. Consequently in these instruments the theory of
closed pipes ceases to be trustworthy when the depth of the whistle
is less than about 60 units. In short, we cannot be sure of sounding
with them a higher note than one of 14,000 vibrations to the second,
unless we use tubes of still smaller bore. 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.
I have tried without much success to produce a note that should be
both shrill and powerful, and correspond to a battery of small
whistles, by flattening a piece of brass tube, and passing another
sheet of brass up it, and thus forming a whistle the whole width of
the sheet, but of very small diameter from front to back. It made a
powerful note, but not a very pure one. I also constructed an
annular whistle by means of three cylinders, one sliding within the
other two, and graduated as before.

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. 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 sound of the individual strings. We all have our limits,
and that limit may be quickly found by these whistles in every case.
The facility of hearing shrill sounds depends in some degree on the
position of the whistle, for it is highest when it 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 the
transmission of rapid vibrations when they strike the ear obliquely.
I myself feel this in a marked degree, and I have long noted the
fact in respect to the buzz of a mosquito