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 situated on the vertical arm of an angular lever whose other arm is the key, t.  When the observer presses the key, the rod, i, again is jerked upward by the spring, h.  The screw, o, tapped into the rod, i, prevents the rod going higher than necessary, by striking a plate, which also serves as guide for i.

To determine the interval between the falling of the ball and pressing of the key, one has finally to count the waves inscribed by the tuning fork, which come under the portion of the line inscribed by s, which is bounded by the two breaks produced by the successive movements of the rod.

To make the glass plate carried by the frame available for more observations, which plate can be used as a photographic negative, the frame, T, is adjustable up and down upon the pillars, N. This frame carries the tuning fork, mercury cup, n, and the electro-magnet, M. The spring, s, can also be moved up and down along the rod, i.—­H.  Heele in Zeitschrift fur Instrumentenkunde.

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A NEW DISINFECTOR.