Circles 3, 4, and 5 sounded together emit the note of circle 2.

(By sounding only two circles, 3 and 4, or 4 and 5, we make the same
experiment with two circles as disk No. 2 enabled us to make with
circle 8 alone; also, by sounding circle 3 alone, we obtain the note
corresponding to 12 holes; then pulling out button 4, the notes
corresponding to 12 and 36 holes are heard suddenly and very strongly;
but as soon as circle 5 is sounded also, the note of 12 disappears
completely, and we have left only that corresponding to 36 holes.)


III.

_Effects of interference produced by shocks in opposite directions_.

1. If we direct against a circle of holes two currents of air in
opposite directions, the note obtained with a single current is very
much weakened, if the two currents reach the holes simultaneously.
If the impulses are not isochronous, the intensity of the note is
increased.

2. If the two currents are directed against two circles of the same
number of holes, the effect is the same as for the two preceding cases.

3. If two currents of air are directed against two circles, one of which
has twice as many holes as the other, we obtain only the low note if
every shock of one is isochronous with every shock of the other.

We obtain the notes of both circles, one of which is the octave of the
other, if there is no isochronism between the shocks.