303-306] MUSICAL INSTRUMENTS 273

306. The Drums. The remaining class of instruments,
the percussion instruments, present few features of interest
that have not been already referred to in the preceding
chapters. With the exception of the Kettle Drums they are
not tuned to any particular notes, and are merely used to
mark the rhythm. The Kettle Drum consists of a hemi-
spherical shell of metal with a skin of parchment stretched over
its open end. The tension of the parchment can be varied by
a number of screws distributed round the rim, and thus the
pitch of the note can be altered. The practicable range of
pitch for any one drum is a fifth. If the parchment is too
slack the tone is bad, and if it is too tight there is a risk of
its being torn. It is most usual to have two drums tuned to
the tonic and dominant of the music, but other numbers of
drums and other notes are often used.
18



QUESTIONS

Many of the following questions are taken from Examination
Papers set in the Universities of Cambridge, London and
Dublin and in the National University of Ireland.
Questions below the line in each section are somewhat more difficult
than those above the line.
CHAPTER I

1. Can sound be propagated through a vacuum ? Describe an
experiment bearing on this question.
2. What characteristics distinguish a musical sound from a
noise 1

3. Describe an experiment from which you conclude that sound
is due to the vibrations of the sounding body. Do all vibrations
give rise to audible sounds ? Illustrate your answer by examples.
