A drum with cogs working by wheels with springs [2].

[Footnote: This chapter consists of explanations of the sketches
shown on Pl. CXXI. Lines 1 and 2 of the text are to be seen at the
top at the left hand side of the first sketch of a drum. Lines 3-5
refer to the sketch immediately below this. Line 6 is written as the
side of the seventh sketch, and lines 7 and 8 at the side of the
eighth. Lines 9-16 are at the bottom in the middle. The remainder of
the text is at the side of the drawing at the bottom.]

A square drum of which the parchment may be drawn tight or slackened
by the lever _a b_ [5].

A drum for harmony [6].

[7] A clapper for harmony; that is, three clappers together.

[9] Just as one and the same drum makes a deep or acute sound
according as the parchments are more or less tightened, so these
parchments variously tightened on one and the same drum will make
various sounds [16].

Keys narrow and close together; (bicchi) far apart; these will be
right for the trumpet shown above.

_a_ must enter in the place of the ordinary keys which have the ...
in the openings of a flute.