3. _In compass._--There are three ways of increasing the compass of the
voice:

1. By the determination of its pitch;
2. By practicing the vocal scale;
3. By the fusion of the registers upon the key-note.

The first of these methods is most effective. The second consists in
exercising upon those notes which are near the key-note. Upon this
exercise depends in great measure the homogeneity of the voice. Taking
_la_ for the diapason, the voice which extends from the lowest notes to
upper _re_ is the chest-voice, since it suffers no acoustic
modification. From _mi_ to _la_ the voice is modified; it is the medium
voice, or the second register, which gives full and supple tones. The
head or throat-voice, or the third register, extends from _si_ to the
highest and sharpest notes. Its tones are weak, and should be avoided
as much as possible. There are then only four good notes--those from
_mi_ to _la_, upon which the voice should be exercised. By uniting the
registers, an artificial, homogeneous voice may be created, whose tones
are produced without compression and without difficulty. This being
done, it is evident that every note of the voice must successively
indicate the three registers--that is, it must be rendered in the chest,
medium and head voices.

There is also a method of diminishing the voice. As the tone is in
proportion to the volume of air in the lungs, it may be weakened by
contracting the epiglottis or by suppressing the respiration.