f you hang a wire from a cord, and hang a heavy weight from the
wire, the wire will be in a state of high tension, and yield a distinct
note if struck. But the volume of sound will be very small, much too
small for a practical instrument. The surface of the string itself is so
limited that it sets up but feeble motions in the surrounding air. Now
hang the wire from a large board and strike it again. The volume of
sound has greatly increased, because the string has transmitted its
vibrations to the large surface of the board.

To get the full sound-value of the vibrations of a string, we evidently
ought to so mount the string that it may influence a large sounding
surface. In a violin this is effected by straining the strings over a
"bridge" resting on a hollow box made of perfectly elastic wood. Draw
the bow across a string. The loud sound heard proceeds not from the
string only, but also from the whole surface of the box.

THE SOUNDING-BOARD AND FRAME OF A PIANO.

A piano has its strings strained across a _frame_ of wood or steel, from
a row of hooks in the top of the frame to a row of tapering square-ended
pins in the bottom, the wires passing over sharp edges near both ends.
The tuner is able, on turning a pin, to tension its strings till it
gives any desired note. Readers may be interested to learn that the
average tension of a string is 275 lbs., so that the total strain on the
frame of a grand piano is anything between 20 and 30 _tons_.

To the back of the frame is attached the _sounding-board_, made of
spruce fir (the familiar Christmas tree). This is obtained from Central
and Eastern Europe, where it is carefully selected and prepared, as it
is essential that the timber should be sawn in such a way that the grain
of the wood runs in the proper direction.

THE STRINGS.

These are made of extremely strong steel wire of the best quality. If
you examine the wires of your piano, you will see that they vary in
thickness, the thinnest being at the treble end of the frame. It is
found impracticable to use wires of the same gauge and the same tension
throughout. The makers therefore use highly-tensioned thick wires for
the bass, and finer, shorter wires for the treble, taking advantage of
the three factors--weight, tension, and length--which we have noticed
above. The wires for the deepest notes are wrapped round with fine
copper wire to add to their weight without increasing their diameter at
the tuning-pins.