nucleus, and the other balls, higher up, represent the medium, which is strictly limited. The gap between these two sets of balls represents the inequality which is to propagate through the medium for a distance of 18″, as soon as the inequality receives an impulse by the removal of the block on the upper chase, when the ball runs down, and, as you see, the nucleus has advanced 18″.
The progress of the action is shown in Fig. 7. The downward slope in the upper chase being uniform for a small distance beyond the position of the stop; then varying, as an inverted S, so as to be horizontal at the level of the lower chase—when the stop is removed the balls start with nearly equal acceleration, then having accelerated, when they reach the steep slope they are separated. And thus the first ball from the upper chase reaches the first ball in the lower chase somewhat ahead of the second ball from the upper chase, and strikes the first ball in the lower chase when it comes to rest without disturbing any of the balls which were in the lower chase except the last, which takes up the motion and runs on towards the basket: the momentum having been conducted through the six balls. Thus the nucleus has advanced in
