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This volume provides an introduction to Borelli´s theory on the movement of animals and describes his theory and scientific experiments relating to the natural movements of bodies in a fluid environment. It describes in great detail why and how bodies which present with different magnitudes, weights and shapes move at a greater or a smaller velocity in certain proportion in the fluid environment.

Originally published in Italian in 1667, then translated into Latin in 1686, the text of this volume has now been translated into English, making the text accessible to a wide readership.

This volume is the second of two volumes that contain the Introduction and physical-mathematical illustrations necessary to understand Giovanni Alfonso Borelli´s work On the Movement of Animals, the founding text of seventeenth century biomechanics. The first volume, entitled On the Force of Percussion , demonstrates the nature of the energy of percussion, its causes, properties and effects.

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Foreword.- Chapter I There are movements of sublunary bodies in a fluid environment, which nobody dealt with so far.- Chapter II On the moments of consistent and fluid heavy bodies floating in fluids.- Chapter III Every fluid body among those which rest on the surface of the earth is heavy and exerts the force of its gravity, even when present and quiescent in its due place, in all the fluid of its kind.- Chapter IV There is no positive lightness in the nature of things.- Chapter V On the structure, the gravity, the equilibrium and the elastic force of air.- Chapter VI There is neither attraction nor attractive force in Nature.- Chapter VII On the nature and cause of fluidity.- Chapter VIII Investigation of the cause of the spontaneous elevation of small particles of water in the air above the surface of the water.- Chapter IX On the mutual binding of floating corpuscles and on their shunning.- Chapter X On the natural velocity of heavy bodies in equal times.- Chapter XI Why movements of heavy bodies are made unequal by full fluid environments.- Chapter XII On the necessity of vacuum.- Chapter XIII Explanation of the fact that watery bodies when they freeze increase in volume with an enormous force.

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