Trumpets and Speaking-Tubes.
How do the waves of sound move?
The waves of sound move in every direction from the place where the noise is made.
Why do we put both hands around the mouth when we call to a person at a distance from us?
We do so to keep the waves of sound more together.
Does it make the voice louder?
It does make the voice louder.
What instrument has been made so as to operate in the same way?
The speaking-trumpet, as is shown in [Fig. 24].
Fig. 24.
Of what use are speaking-trumpets?
They are of much use to firemen when giving orders at a fire, and to those on board of vessels when giving orders to the sailors.
Why do we hold the hand behind the ear when we wish to hear more distinctly?
Because the hand catches more of the waves of sound, and conducts them to the ear.
What instrument has been made to serve the same purpose?
The ear-trumpet, as is shown in [Fig. 25].
Fig. 25.
How does the ear-trumpet aid the hearing?
The large end of the trumpet collects more of the waves of sound than the ear can; hence, more waves reach the ear.
Why do such animals as the horse, the rabbit, and the deer, hear better than we do?
Because their large ears act like ear-trumpets to collect the waves of sound, and thus increase their faculty of hearing.
How can these animals still farther increase their sense of hearing?
By being able to turn their ears, just as we do the ear-trumpet, in the direction whence the sound comes.
What are speaking-tubes?
They are metal pipes extending from one part of a building to another part.
Of what use are speaking-tubes?
They are used to convey the voice to the more distant parts of a building.
Do they require loud talking?
No; even a whisper has been heard through a metal pipe over three thousand feet long.