g the pressure of the wind,
as is also the case with the double reed or the single or beating reed,
while the pressure of the reed with the lips combined with greater
pressure of wind produces the harmonic overtones which are not given out
by free reeds. The English concertina possesses one peculiarity which
renders it unsuitable for playing with instruments tuned according to
the law of equal temperament, such as the pianoforte, harmonium or
melodion, i.e. it has enharmonic intervals between G# and A# and between
D[flat] and E[flat]. The German concertina is not constructed according
to this system; its compass extends down to C or even B[flat], but it is
not provided with double action. It is possible on the English
concertina to play diatonic and chromatic passages or arpeggios in
legato or staccato style with rapidity, shakes single and double in
thirds; it is also possible to play in parts as on the pianoforte or
organ and to produce very rich chords. Concertos were written for
concertina with orchestra by Molique and Regondi, a sonata with piano by
Molique, while Tschaikowsky scored in his second orchestral suite for
four accordions.

The aeola, constructed by the representatives of the original firm of
Wheatstone, is a still more artistically developed concertina, having
among other improvements steel reeds instead of brass, which increase
the purity and delicacy of the timbre.

See also ACCORDION; CHENG; HARMONIUM; Free-Reed Vibrator. (K. S.)

CONCERTO (Lat. _concertus_, from _certare_, to strive, also confused
with _concentus_), in music, a term which appears as early as the
beginning of the 17th century, at first as a title of no very definite
meaning, but which early acquired a sense justified by its etymology and
became applied chiefly to compositions in which unequal instrumental or
vocal forces are brought into opposition.

Although by Bach's time the concerto as a polyphonic instrumental form
was thoroughly established, the term frequently appears in the autograph
title-pages of his church cantatas, even when the cantata contains no
instrumental prelude. Indeed, so entirely does the actual concerto form,
as Bach understands it, depend upon the opposition of masses of tone
unequal in volume with a compensating inequality in power of commanding
attention, that Bach is able to rewrite an instrumental movement as a
chorus without the least incongruity of style. A splendid example of
this is th