SECTION XII.. The Vibrations Must Be Similar.

THE VIBRATIONS MUST BE SIMILAR.

But if the vibration be not similar at every impression, it can never be carried beyond the number of actual impressions; for, move any body as a pendulum, in one way, and it will continue to oscillate in an arch of the same circle, until the known causes make it rest; but if, after first putting it in motion in one direction, you push it into another, it can never reassume the first direction; because it can never move itself, and consequently it can have but the effect of that last motion; whereas, if in the same direction you act upon it several times, it will describe a greater arch, and move a longer time.