CHAPTER IV.

THE TONES ABOUT US.


"Scientific education ought to teach us to see the invisible as well
as the visible in nature."--_John Tyndall_.[10]

There used to live in England a famous scientist named Tyndall, who
was interested, among other things, in the study of sound. He studied
sounds of all kinds, made experiments with them, wrote down what he
observed, and out of it all he wrote a book,[11] useful to all who
desire to learn about sound and its nature.

One day, Tyndall and a friend were walking up one of the mountains of
the Alps.[12] As they ascended the path, Tyndall's attention was
attracted by a shrill sound, which seemed to come from the ground at
his feet. Being a trained thinker he was at once curious to know what
was the cause of this. By looking carefully he found that it came from
a myriad of small insects which swarmed by the side of the path.
Having satisfied himself as to what it was he spoke to his companion
about the shrill tone and was surprised to learn that he could not
hear it. Tyndall's friend could hear all ordinary sound perfectly
well. This, however, seemed to be sound of such a character as did not
reach his sense of hearing. One who like Tyndall listened carefully to
sounds of all kinds would quickly detect anything uncommon. This
little incident teaches us that sounds may go on about us and yet we
know nothing of them. Also it teaches us to think about tones, seek