p called
Dulciana. Wider pipes do not require to be so long in order to produce
8-ft. tone.

"If a tube * * * open at both ends be blown across at one end, the
fundamental tone of the tube will be sounded; but if the hand be placed
at one end of the tube, so as to effectually close it, and the open end
be blown across as before, a sound will be heard exactly one octave
below that which was heard when both ends of the tube were open. One
of these pipes was an open pipe, the other a stopped pipe; and the
difference between the two is that which constitutes the two great
classes into which the flue pipes of organs are divided." [1]

Thus by stopping up the end of an organ pipe we get 8-ft. tone from a
pipe only 4 ft. long, 16-ft. tone from a pipe 8 ft. long, and so on,
but with loss of power and volume. The harmonics produced from stopped
pipes are entirely different from those of the open ones; their
harmonic scale is produced by vibrations which are as 1, 2, 3, 4, etc.,
those of a stopped pipe by vibrations which are as 1, 3, 5, 7. All
these harmonics are also called upper partials.

The Estey Organ Company claim to have discovered a new principle in
acoustics in their Open Bass pipes, of which we show a drawing
opposite. This invention (by William E. Haskell) enables the builders
to supply open bass tone in organ chambers and swell boxes where there
is not room for full-length pipes.

[Illustration: Fig. 16. Estey's Open Bass Pipes--Wood and Metal]

Referring to the illustration, it will be seen that the pipes are
partly open and partly stopped, with a tuning slide in the centre. The
builders write as follows:

"The inserted tube, or complementing chamber, in the pipe is such in
length as to complete the full length of the pipe. It is, as will be
noted, smaller in scale than the outside pipe. The effect is to
produce the vibration that would be obtained with a full-length pipe,
and in no way does it interfere with the quality of tone. In fact, it
assists the pipe materially in its speech. This is most noticeable in
a pipe such as the 32-foot Open Diapason, which when made full length
is quite likely to be slow in speech. With this arrangement the pipe
takes its speech very readily and is no slower in taking its full
speech than an ordinary 16-foot Open Diapason.

"We have worked this out for all classes of tone--string, flute and
diapason--and the law holds good in every instance."

Helmholtz was t