"If you throw two small stones at the same time on a sheet of motionless water at some distance from each other, you will observe that around the
two percussions numerous separate circles are formed; these will meet as they increase in size and then penetrate and intersect one another, all the
while maintaining as their respective centres the spot struck by the stones. And the reason for this is that the water, although apparently moving,
does not leave its original position, because the opening made by the stones closes again immediately. Therefore the motion produced by the quick
opening and closing of the water has caused only a shock which may be described as a tremor rather than movement. In order to understand better what I
mean, watch the blades of grass that because of their lightness float on the water, and observe how they do not depart from their original positions in
spite of the waves underneath them caused by the occurrence of the circles. The reaction of the water being in nature of tremor rather than movement,
the circles cannot break one another on meeting, and as the water is of the same quality all the way through, its parts transmit the tremor to one
another without change of position. Thus the water, although remaining in its position, can easily transmit the tremor to the adjacent parts, these
transmitting it to other adjacent parts, while its force gradually diminishes until the end."
Leonardo da Vinci
Manuscript A, Institute de France, Paris
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