4 
Bird~Song : and New Zealand Song Birds 
less complex. It vibrates as a whole; and this, the principal 
vibration, gives the principal and predominant note. At the 
same time, it vibrates in two equal parts, each vibrating with 
twice the frequency of the whole, and producing accordingly 
a note an octave higher, but very much fainter, than the prin¬ 
cipal note. Nor is this all. The wire or string, supposing it to 
be a piano or violoncello, or other stringed instrument, in 
question, is subdivided into quite a number of portions, all 
vibrating with different frequency from the whole string, and 
so producing different sounds. All are normally, however, 
vibrating in definite and comparatively fixed proportions. The 
string is, as it were, divided first into two portions; then into 
three, four, five, six, and so on. Where the division is into two 
the vibrating parts give a sound an octave above the principal 
note, their rates of vibration being double that of the full 
string; where the division is into three, the vibrating parts 
give a sound a twelfth above the principal note, or a fifth above 
the first octave; where the division is into four, the vibrating 
portions give a sound two octaves above the principal note, as 
their rates of vibration are four times that of the full string; 
where it is into five, a sound a seventeenth above the principal 
note, or a third above the second octave; and so on. The full 
note is, in fact, composed of quite a number of different sounds, 
called harmonics or partial tones. WTrilst they are present 
they are exceedingly faint, the smaller the subdivision pro¬ 
ducing them the fainter being the sound emitted, and the 
less distinguishable from the much fuller body of the principal 
note. The ordinary unaided ear is able to detect the first four 
or five partial tones only; yet the presence or absence of these 
and the higher partials determines the richness and quality of 
the resultant sound. The vibration of different materials pro¬ 
duces different partials, or produces them in different degrees 
of intensity: the human voice is rich in the lower partials; in 
cymbals and like “ noisy ” instruments the upper * partials 
predominate. The nasal quality of the oboe and clarinet is 
caused by the absence of the even partials—the second, fourth, 
sixth—and the presence of the odd—the first, third, fifth, 
seventh. 
