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connected with iron finger-boards; on pressing down
which, the communication between the chest and the
channels is opened. Along the channels is a range of
holes corresponding with others on an upper table, called
rivag in Greek. Between this table and the canon, rules
are interposed, with corresponding holes well oiled, so
that they may be easily pushed up and return; they are
called pleuritides, and are for the purpose of stopping
and opening the holes along the channels, which they
do by passing backwards and forwards. These rules
have iron jacks attached to them, and being united to
the keys, when those are touched they move the rules.
Over the table there are holes through which the wind
passes into the pipes. Rings are fixed in the rules, for
the reception of the feet of the organ-pipes. From the
barrels run pipes joined to the neck of the wind-chest,
which communicate with the holes in the chest, in
which pipes are closely fitted valves ; these, when the
chest is supplied with wind, serve to close their orifices,
and prevent its escape. Thus, when the levers are
raised, the piston-rods are depressed to the bottom of the
barrel, and the dolphins turning on their pivots, suffer
the valves attached to them to descend, thus filling with
air the cavities of the barrels. Lastly ; the pistons in
the barrels being alternately raised and depressed with
a quick motion, cause the valves to stop the upper holes :
the air, therefore, which is spent, escapes into the pipes,
through which it passes into the wind-chest, and thence,
by its neck, to the box. By the quick motion of the
levers still compressing the air, it finds its way through
the apertures of the stops, and fills the channels with
wind. Hence, when the keys are touched by hand, they
propel and repel the rules, alternately stopping and
opening the holes, and producing a varied melody
founded upon the rules of music. I have done my
utmost to give a clear explanation of a complex ma-
chine. This has been no easy task, nor, perhaps, shall
