s, entailing the use of the
lower and middle strings are only permissible as embellishments.
Glissando passages in chords of the seventh and ninth, enharmonically
obtained, are much more common, and as the above reservations do not
apply, every dynamic shade of tone is possible. Chords in harmonics
can only consist of three notes written close together, two for the
left hand and one for the right.

The tender poetic quality of the harp is adapted to every dynamic
shade, but it is never a very powerful instrument, and the
orchestrator should treat it with respect.

At least three, if not four harps in unison are necessary, if they are
to be heard against a full orchestra playing _forte_. The more rapidly
a _glissando_ passage is played, the louder it will sound. Harmonic
notes on the harp have great charm but little resonance, and are only
possible played quite softly. Speaking generally, the harp, like the
string quartet, _pizzicato_, is more an instrument of colour than
expression.

Percussion instruments producing determinate sounds, keyed
instruments.

Kettle-drums.

Kettle-drums, indispensable to every theatre and concert orchestra
occupy the most important place in the group of percussion
instruments. A pair of kettle-drums (_Timpani_), in the tonic and
dominant keys, was the necessary attribute of an orchestra up to, and
including Beethoven's time, but, from the middle of the 19th
century onward, in western Europe and in Russia, an ever-increasing
need was felt for the presence of three or even four kettle-drums,
during the whole course or part of a work. If the expensive chromatic
drum, permitting instant tuning is rarely met with, still, in the
majority of good orchestras, three screw drums are generally to be
found. The composer can therefore take it for granted that a good
timpanist, having three kettle-drums at his command, will be able to
tune at least one of them during a pause of some length.

The limits of possible change in Beethoven's time was considered to
be:

Big kettle-drum: [Music: F2-C3 (chromatically)]
Small kettle-drum: [Music: B[flat]2-F3 (chromatically)]

In these days it is difficult to define the precise extent of high
compass in the kettle-drums, as this depends entirely on the size and
quality of the smallest one, of which there are many kinds, but I
advise the composer to select:

[Music: E2-G[sharp]3 (chromatically)]

_Note._ A magnificent kettle-drum of very small