John Freely

John Freely (26 June 1926 – 20 April 2017) was an American physicist, teacher, and author of popular travel and history books on Istanbul, Athens, Venice, Turkey, Greece, and the Ottoman Empire.

Quotes

Before Galileo, The Birth of Modern Science in Medieval Europe (2012)

• John Philoponus (c. 490-570) of Alexandria... refuted Aristotle's theory that the velocities of falling bodies in a given medium are proportional to their weight, making the observation that "if one lets fall simultaneously from the same height two bodies differing greatly in weight, one will find that the ratio of the times of their motion does not correspond to the ratios of their weights, but the difference in time is a very small one." …He also criticized Aristotle's antiperistasis theory of projectile motion, which states that the air displaced by the object flows back to push it from behind. Instead Philoponus concluded that "some incorporeal kinetic power is imparted by the thrower to the object thrown" and that "if an arrow or a stone is projected by force in a void, the same will happen much more easily, nothing being necessary except the thrower." This is the famous "impetus theory," which was revived in medieval Islam and again in fourteenth century Europe, giving rise to the beginning of modern dynamics.
  • p. 8

• Newton's proof of the law of refraction is based on an erroneous notion that light travels faster in glass than in air, the same error that Descartes had made. This error stems from the fact that both of them thought that light was corpuscular in nature.
  • p. 189

• Although many historians of the new millennium now take issue with the notion of a Scientific Revolution, it is generally agreed that Newton's work culminated the long development of European science, creating a synthesis that opened the way for the scientific culture of the modern age.
  • p. 190

• Parmenides believed that all Being is what he called the One, and denied absolutely the possibility of change. He believed that the cosmos is full (i.e., no void), uncreated, eternal, indestructible, unchangeable, immobile sphere of being, and all sensory evidence to the contrary is illusory. One Parmenidean fragment stated, "Either a thing is or it is not," meaning that creation and destruction is impossible.
  • p. 286

• The atomic theory was not generally accepted in the time of Democritus, largely because of its deterministic character, for it allows no chance, choice, or free will.
  • p. 287

• Empedocles tried to address the problem of change by saying that there is not one fundamental arche but four—earth, water, air, and fire—which generate all the material substances in nature by mixing together in various ways under the influence of forces he called Love and Strife.
  • p. 287

• Anaxagoras of Clazomenae (0. 500—428 BC) postulated another element called the aether, which was in constant rotation and carried with it the celestial bodies. He also believed that there was a directing intelligence in nature that he called Nous which gives order to what otherwise would be a chaotic universe. By Nous he meant literally "the Mind of the Cosmos"… Anaxagoras was the last of the Ionian physicists.
  • p. 287

• The dominant concept in Aristotle's philosophy of nature is his notion of causation. ...The final cause states that each substance has an inherent purpose. Thus there must be a purpose or design in the acorn such that it always grows into an oak tree. This aspect of existence is indicated by the word entelechy; this means the purpose that guides things to develop in one way rather than another.
  • p. 291