THE AUTHOR'S

PREFACE

The senior mechanicians understood in some part that the force and energy of percussion is not small, but of immense power; this can be conjectured from those things which Aristotle left to posterity. For in his Mechanical Problems original: "in mechanicis", by his own sagacity, he noticed that motion is the cause of the energy of percussion, and that the force of percussion increases all the more as the velocity of the striking body increases. He did not, however, deeply perceive or attain the nature of percussion; for he says that motion increases and adds weight to heavy bodies, and that impetus is a certain flowing gravity. And because the action of gravity is a certain compression and impulse, he thought that the most vehement compression we observe in percussion arises from that same power of gravity, increased and multiplied by motion and impetus. I have sufficiently explained the falsity of this opinion in its proper place. Although this very problem has been attempted by many after Aristotle, no one has resolved it or penetrated its recesses, from which it can therefore be conjectured how difficult it is and how obscured by shadows.

Later, the renowned Galileo, in a mechanical booklet published in his youth, brought forward a sufficiently plausible cause for the energy of percussion, taken from that most common principle and mechanical maxim: that the momentum of the power is then equal to the momentum of the resistance when their velocities are reciprocally proportional to the powers. That is, the resistance of any vast body is overcome and raised by the strike of a smaller body, because a velocity is communicated to it which has the same proportion to the velocity of the striker as the power of the striker has to the resistance of the struck body. But later, that most perspicacious man perfectly perceived the insufficiency of his youthful reasoning. For it is true in a balance or similar mechanical instrument that unequal weights can respond proportionately to their velocities in inverse order, the lack of weight being compensated by an excess of velocity, and then their momenta are equal. But the business of percussion proceeds in a far different manner. For first, we are ignorant of what the power of the striker and the resistance of the struck body are, and in what they consist. For according to Galileo's reasoning, it must be granted that the percussive power is far different from the motion, velocity, or impetus by which striking bodies are agitated. For if percussive power and its velocity were the same thing, it would have