Introduction 3 
song* to be out of tune, why do not the songs of birds sound 
out of tune ? The very fact that they are tuneful and pleasing 
to practically every human ear is surely fact sufficient to give 
one pause before stating that their notes do not conform 
to the scale accepted by musicians. Did they not conform, 
their sound would be found intolerable, simply because they 
would be different from the standard to which we are accus¬ 
tomed. They are, of course, full of slurs, trills, vocalizations, 
changes of timbre, to an extent quite beyond the human voice 
or any single musical instrument; but the basis on which they 
are built is none other than that on which the music of the 
human voice and of musical instruments is built, and the one 
notation serves for recording them all. It is true the birds do 
not confine themselves to tones and semitones; they use these, 
but many intermediate divisions as well. 
The scale in music is usually considered to be an artificial 
subdivision of a range of sound lying between two notes, one 
of which is composed of twice the number of vibrations per 
second that composes the other. This range is called an octave, 
and it comprises seven different notes, rising in pitch in a 
definite series from the lowest to the highest. The eighth 
note lias a difference in pitch from the lowest, and a certain 
difference in sound; though if the two are sounded together a 
single appreciable sound results: their vibrations coincide, 
and, in addition to the coinciding vibrations, the higher note 
bas an additional vibration midway between each coinciding 
paii , so that whilst one sound results when both notes are 
sounded together, the ear is easily able to detect its composite 
quality. 
T\ lien, then, two notes, one an octave higher than the other, 
aie sounded together, the singleness of the sound is apparent 
only. It is quite evident that there must be two sounds in the 
resultant note, and the ear is easily able to detect both. Fur¬ 
thermore, if the lower note be sounded alone, the ear is still 
able to detect the upper, though with much greater difficulty 
than when both are sounded together. Nor is this imagination 
only. The motion of every resonant vibrating body is more or 
