will find them a great source of revenue, as they are
almost invariably in need of repair.

Compare the three cuts of actions in the study of this lesson.

The main constituent parts of the square action are similar in
appearance to those of the upright; in fact, most of the parts are
the same in name and office. However, the parts are necessarily
assembled very differently. In the square action, the hammers strike
in a vertical direction, while in the upright they strike in a
horizontal direction; the motion of the key being the same in both.

Of the three types, the square is the simplest action, as many of the
parts seen in the upright and grand are entirely absent in the square.

Beginning with the key, it has its balance pin, guide pin, cushions,
etc., practically the same as in the other types.

The bottom, or key rocker, is reversed in the square; the end
transmitting the motion being nearest the performer.

The extension and wippen are absent in the square, as the jack is
attached directly to the bottom or key-rocker.

The back check is screwed to the key, and as the hammer head rests
against it after striking, the use of the contrivance called the back
catch in the upright is unnecessary.

[Illustration: ACTION OF THE SQUARE PIANO.]

ACTION OF THE SQUARE PIANO.

A. Action Frame.

B's Indicate the Cushions, or Bushing, of felt, cloth or leather.

C. Balance Rail.

D. Balance Pin. Round.

E. Mortised Cap for Balance Pin. Bushed.

F. Key.

G. Lead.

H. Back Check.

I. Bottom or Key Rocker.

J. Bottom Screws; used to regulate height of Jack.

K. Jack.

L. Jack Spring; concealed under Bottom.

M. Center Pin to Jack.

N. Hammer Rail.

O. Regulating Screw.

P. Regulating Button.

Q. Flange Rail.

R. Flange. Split.

S. Flange Rail Screw.

T. Flange Screw, to regulate jaws of flange.

U. Hammer Butt.

V. Center Pin.

W. Hammer Stem or Shank.

X. Hammer Head.

Y. Hammer Felt. Treble hammers sometimes capped with buckskin in
old instruments.

TOP ACTION OF SQUARE PIANO.

1. Damper Lifter Wire.

2. Damper Lifter Buttons.

3. Damper Felt.

4. Damper Head.

5. Damper Lever.

6. Damper Leads.

7. Shade, supported by wire stanchions, on top of which are
screwed shade buttons.

8. Damper Rail. Tilted by Loud Pedal Ro