THE VOICES OF NATURE. 
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C fork only moves twice; therefore the G fork does 
not crowd so many atoms together before it draws 
back, and the waves are shorter. These two notes, C 
and G, are a fifth of an octave apart; if we had two 
FIG. 37. 
forks, of which one went twice as fast as the other, 
making four waves while the other made two, then 
that note would be an octave higher. 
So we see that all the sounds we hear the warning 
noises which keep us from harm, the beautiful musical 
notes with all the tunes and harmonies that delight 
us, even the power of hearing the voices of those we 
love, and learning from one another that which each 
can tell all these depend upon the invisible waves of 
air, even as the pleasures of light depend on the waves 
of ether. It is by these sound-waves that nature 
speaks to us, and in all her movements there is a 
reason why her voice is sharp or tender, loud or gentle, 
awful or loving. Take for instance the brook we 
spoke of at the beginning of the lecture. Why does 
it sing so sweetly, while the wide deep river makes 
