27. The kettle-drum is the most important member of the percussion family and is always used either in pairs or in threes. The size of these instruments varies somewhat with the make, but when two drums are used the diameter is approximately that given under the illustration. The range of a pair of drums is one octave
and when but two drums are used the larger one takes the tones from F to about C of this range, and the smaller takes those from about B♭ to F. The most common usage is to tune one drum to the tonic, and the other to the dominant of the key in which the composition is written. The pitch of the kettle-drum can be varied by increasing or lessening the tension of the head by means of thumb-screws which act on a metal ring.
The other important members of the percussion family are shown on this and the following page, their use being so obvious as to require no detailed explanation.
