galton.org 27
Whistles for Audibility of Shrill Notes
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the experiment quickly shows that they are absolutely deaf to shrill notes
which the younger persons hear acutely, and they commonly betray much
dislike to the discovery. Every one has his limit, and the limit at which
sounds become too shrill to be audible to any particular person can be
rapidly determined by this little instrument. Lord Rayleigh and others
have found that sensitive flames are powerfully affected by the vibrations
of whistles that are too rapid to be audible to ordinary ears.
I have tried experiments with all kinds of animals on their powers of
hearing shrill notes. I have gone through the whole of the Zoological
Gardens, using an apparatus arranged for the purpose. It consists of one of
my little whistles at the end of a walking-stick—that is, in reality, a long
tube; it has a bit of India-rubber pipe under the handle, a sudden squeeze
upon which forces a little air into the whistle and causes it to sound. I hold
it as near as is safe to the ears of the animals, and when they are quite
accustomed to its presence and heedless of it, I make it sound; then if they
prick their ears it shows that they hear the whistle; if they do not, it is
probably inaudible to them. Still, it is very possible that in some cases
they hear but do not heed the sound. Of all creatures, I have found none
superior to cats in the power of hearing shrill sounds; it is perfectly
remarkable what a faculty they have in this way. Cats, of course, have to
deal in the dark with mice, and to find them out by their squealing. Many
people cannot hear the shrill squeal of a mouse. Some time ago, singing
mice were exhibited in London, and of the people who went to hear them,
some could hear nothing, whilst others could hear a little, and others again
could hear much. Cats are differentiated by natural selection until they
have a power of hearing all the high notes made by mice and other little
creatures that they have to catch. A cat that is at a very considerable
distance, can be made to turn its ear round by sounding a note that is too
shrill to be audible by almost any human ear. Small dogs also hear very
shrill notes, but large ones do not. I have walked through the streets of a
town with an instrument like that which I used in the Zoological Gardens,
and made nearly all the little dogs turn round, but not the large ones. At
Berne, where there appear to be more large dogs
