he first to demonstrate that the _quality_ of all
musical tones depends entirely upon the presence or absence of their
upper partials. In the hollow tone of the Flute they are almost
entirely absent; in the clanging tone of the Trumpet many of the higher
ones are present; and if we take an instrument like the Cymbals we get
the whole of the upper lot altogether.

The different qualities of tone of the organ pipes are therefore
determined: (1) By the material of which the pipes are made; (2) by the
shape of the pipe; (3) by the amount of wind pressure; (4) by the shape
and size of the mouth, the relation of the lip to the stream of wind
impinging on it from a narrow slit, and the shape and thickness of the
lip itself. The manipulation of the mouth and lip to produce the tone
desired is called voicing and calls for considerable artistic skill.
The writer recollects an instance of a clever voicer (Gustav Schlette)
taking a new organ in hand, which was not quite satisfactory, and on
the following Sunday he hardly knew it again.

Another kind of harmonics must now be described, called combinational
or Tartini tones (from Tartini, a celebrated Italian violinist of the
XVII century, who first described them). "These tones," says
Helmholtz, "are heard whenever two musical tones of different pitches
are sounded together loudly and continuously." There is no necessity
for giving a table of all of their tones here; we select the two most
useful. If two notes at an interval of a fifth are held down, a note
one octave below the lower one will be heard. So organ builders take
two pipes--one 16 feet long (CCC) and one 10 2/3 feet long (GG)--which
make the interval of the fifth, and, by sounding them together, produce
the tone of a pipe 33 feet long (CCCC). This is the stop which will be
found labeled "32-ft. Resultant." Hope-Jones makes a stop which he
calls Gravissima, 64-ft. Resultant, in his large organs. Many contend
that this system produces better results than if pipes of the actual
lengths of 32 or 64 feet were employed. Indeed, a pipe 64 feet long
would be inaudible; the human ear has its limitations and refuses to
recognize tone lower than 32 feet (just as we cannot lift water by a
suction pump over 32 feet)--_but_, these great pipes _produce
harmonics_ which wonderfully reinforce the tone of the organ.
Therefore their use is worth while.

The other combinational tone to which we refer is that produced by the
int