magnetism thus excited, the arms of the tuning fork are attracted by
the poles of the magnet, and forced to beat with increased amplitude.
In a short time a constant amplitude of oscillation is reached, when
the magnetic impulses are of equal influence with the atmospheric
resistance and the internal force of the tuning fork restraining its
movements.

Finally, the stylus, _s_, which touches the glass plate directly above
_y_, is for registering the moments when by the falling ball the sound
is produced and when the observer presses the key. This is brought
about by the rod, _i_, to which _s_ is firmly screwed, being jerked
upward a short distance at each of these instants, so that the
horizontal lines which the stylus, _s_, marks upon the screen passing
in front of it are broken at both places.

The mechanism which jerks the rod, _i_, upward is thus arranged: The
inclined plate, _p_, on which the ball drops, is carried by the upper
horizontal arm of an angular lever turning on the axis, _x_, and
counterpoised by the balancing weight, _x'_. By the falling ball this
arm is pressed downward, and the lower horizontal arm, _w_, of the
lever is also moved. On a second horizontal axis the lever, _v_,
partly concealed, moves, restricted as to its length of swing by the
screws, _n_. As long as the concealed arm is not moved, _v_ is lightly
pressed by the small spring, _e_, against _w_. The projection, _z_, at
the upper end of _v_ holds the rod, _i_, which the strong spring, _h_,
is continually pressing upward. When the ball falls upon the plate,
_p_, the arm, _w_, presses against the lower end of _v_, the
projection, _z_, sets free the rod, and it springs upward. This
movement is soon arrested, as the projection, _z'_, engages with a
stud situated on the right side of the rod, _i_. This projection is