Now it is a law of friction that you cannot have
friction between two back legs if the back legs are not touching; in
other words the grasshopper does not rub his back legs together to
produce stridulation, or, to put it quite shortly, he does not rub his
back legs together _at all_. I hope I have made this point quite clear.
If not, a more detailed treatment will be found in the Paper which I
read to the Royal Society in 1912.
Nevertheless I have always felt that there was something fishy about the
grasshopper's back legs. I mean, why _should_ he wave his back legs
about when he is stridulating? My own theory is that it is purely due to
the nervous excitement produced by the act of singing. The same
phenomenon can be observed in many singers and public speakers. I do not
think myself that we need seek for a more elaborate hypothesis. _The
Encyclopaedia Britannica_, of course, says that "the stridulation or song
in the _Acridiidae_ is produced by friction of the hind legs against
portions of the wings or wing-covers," but that is just the sort of
statement which the scientific man thinks he can pass off on the public
with impunity.
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