as we have seen, is a
gradual change in the key while the voice is speaking. The pitch or
key depends upon the muscular tension of the vocal chords, which act
like the strings of a musical instrument: the greater the tension, the
higher the key. Muscular tension implies nervous tension and this is
dependent upon the mental state. If the mind is calm, the nervous and
muscular tension is normal, and the speaker uses the key habitual to
him in his ordinary speech. If the mental state is one of excitement,
the key is higher because of greater nervous and muscular tension. If,
on the other hand, the mental state is one of depression, the key is
lower because of relaxed muscular tension.

In _The Defence of the Bridge_ (p. 206) the Romans, seeing the danger
of the heroes, are wrought up to a high state of nervous tension which
finds its natural expression in the high-pitched voice:

"Come back, come back Horatius!"
Loud cried the Fathers all.
"Back, Lartius! back Herminius!
Back, ere the ruin fall!"

Contrast with this the lower key of Horatius, who is calm and
self-controlled:

"O Tiber! Father Tiber!
To whom the Romans pray,
A Roman's life, a Roman's arms,
Take thou in charge this day!"

Observe the gradual rise in pitch with the increase of tension or
excitement in the following:

And now he feels the bottom;
Now on dry earth he stands;
Now round him throng the Fathers
To press his gory hands;
And now, with shouts and clapping,
And noise of weeping loud,
He enters through the River-Gate,
Borne by the joyous crowd.

In the following lines, where the Douglas holds communion with
himself, the tension is low chiefly because of his great mental
depression, and, consequently, he speaks in a low key:

Yes! all is true my fears could frame;
A prisoner lies the noble Graeme,
And fiery Roderick soon will feel
The vengeance of the royal steel.
I, only I, can ward their fate,--
God grant the ransom come not late.
The abbess hath her promise given.
My child shall be the bride of Heaven:--
Be pardoned one repining tear!
For he, who gave her, knows how dear,
How excellent! but that is by,
And now my business is--to die.

The low pitch is also partly due to the fact that the Douglas is
speaking to himself, and has no desire to communicate his thoughts to
another; for the effort to communicate thought causes increased
tension.

Again, it requ