Main Catalogue - VUOTOTECNICA - #5

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4 MIDDLE AGES During the 5th century, John Philoponus criticised the Aristotelian theory on vacuum and laid the foundations of the impetus theory of the 13th and 14th century. According to Philoponus, a projectile moves on account of an incorporeal kinetic force which is impressed on it when it is released (prefiguration of what nowadays is called momentum) and the medium’s resistance to motion is reduced to a simple additional element. This way, motion in a vacuum becomes possible. Around the 10th and 11th century, the debate on vacuum involved Arab scholars and commentators who contributed to the development of the impetus theory. In particular, Ibn Sina, aka Avicenna took up John Philopunus’ ideas adding an important element. According to Avicenna, the force impressed at the start of the motion in a vacuum, never ceases, therefore, motion continues indefinitely. On the other hand, famous Aristotelian commentator Averroes (12th century), rejected this theory, stating that motion always occurs through a medium, therefore, turning to an hypothetical incorporeal force meant searching the cause of things in an imaginary world instead of in reality. Since the first half of the 13th century, these disputes moved from the Islamic world back to the Western world, involving some of the brightest minds of that period (from Albert the Great to Thomas Aquinas). The broadening of Philoponus’ and Ibn Bajjas’ (aka Avempace), finally led to the systematic elaboration of the impetus theory, one of the most important results of the Paris school. modern AGE In 1644, Descartes published Principles of Philosophy, where he argued against the existence of vacuum. The fact that air has a mass and is therefore subject to Earth’s gravitational attraction, was acknowledged that same year, when Evangelista Torricelli (1608-1647) Italian physicist and disciple of Galileo Galilei, described the famous experiment with the glass tube full of mercury, with the open end placed inside a basin also containing mercury. Until then, the Aristotelian theory of “horror vacui” had still been en vogue. Torricelli sensed that the force that held the mercury column up inside the glass tube was not due to “horror vacui”, but depended on the pressure that the air exerted on the mercury in the basin. On the other hand, the water that went up the tube from which air was sucked, did so, not because it had to fill the void abhorred by nature, but because pushed by the air pressure exerted on the water. Torricelli not only provided a new hypothesis to explain the phenomenon he had observed, but he also suggested an experiment to confirm his idea. This experiment consisted in measuring the height of the mercury column inside the glass tube in a high mountain area. Renè Descartes (Cartesio) (1596 - 1650) Evangelista Torricelli portrayed on the front page of Lezioni accademiche di Evangelista Torricelli, Florence (1715) Cartesian vortexes R. Descartes, Principles of Philosophy (1644)