[Side note: How use the lungs]

We now come to the important question--How shall I increase my
vocal powers? As is well known, there are two methods of inhaling
and expelling the air from the lungs. One is by means of the
rising and falling of the ribs. This is called "the costal
method." The other is by the contraction and distention of the
midriff or diaphragm. The diaphragm is the movable floor to the
thorax or box that encloses the lungs. This is called "the
diaphragmatic method." Now, since God has furnished us with both
methods, He evidently intended that we should use both, as we use
our two eyes or our two ears. They are given, not as alternative,
but as simultaneous instruments of action. The weakness in many a
speaker's voice, its want of volume and its failure when a
sustained effort is demanded, is due to the fact that he breathes
by means of his ribs alone, throwing all the pressure on the
upper portion of the lungs, not asking the large areas to
contribute anything. He thus robs himself of breathing capacity,
and consequently of voice power.

[Side note: Diaphragmatic breathing]

To get a perfect mastery over the "diaphragmatic" method and make
it as serviceable as possible, practise breathing while lying on
your back, filling the lungs to the utmost, and exhausting them
as completely as possible. Inhale rapidly and exhale slowly. Then
reverse the order; inhale slowly and exhale rapidly. Again let
"slow" and "rapid" alternately make both movements.

By this exercise you acquire flexibility of the midriff muscles,