Chapter 11.

Galileo and Decartes

11.1. Galileo Galilei (1564-1642)

• Born in Pisa in year of Shakespeare's birth and Michelangelo's death
• Father later a musician for Medici's in Florence
• Educated in Medici household; studied in Rome; later studied medicine at University of Pisa, did not graduate
• Appointed professor of mathematics in Pisa in 1589 at age 26; not re-appointed at Pisa; appointed professor of mathematics at University of Padua in 1592, where he remained for 18 years
• Devised working telescope in 1609 on basis of having heard of invention in Holland
  • Discoveries and observations with telescope
    • Jupiter's four large satellites
    • Craters and mountains on Moon
    • Phases of Venus
    • Milky Way composed of individual faint stars
    • Observes sunspots (not new)
  • Published discoveries in Starry Messenger in 1609
• Mechanics
  • Argues against Aristotelian mechanics
  • Any body set into motion will continue to move indefinitely at the same speed and in the same direction (law of inertia)
  • Concept of force bringing about change in motion of bodies
  • In free fall through a vacuum, all objects--of whatever weight, size, or constitution--will fall a given distance in the same time
  • Free fall motion is uniformly accelerated motion, i.e., it gains equal increments of speed in equal times, or distance is proportional to time squared
  • Pendulum swings with a period depending on its length but not the weight of its bob
  • Earth exerts influence on a body in free fall or rolling down an inclined plane - gravity
  • Projectile motion is motion along a parabola, symmetric about the highest point
  • Galileo brings together strands of medieval thought regarding space, time, and motion
  • Published in 1632 in Dialogues on the Two Great World Systems and in 1638 in Discourses and Mathematical Demonstrations Concerning Two New Sciences Pertaining to Mechanics and Local Motion

11.2. René Descartes (1596-1650)

• Born in Bretagne, France in 1596; son of well-to-do counselor in parliament in Bretagne
• Educated in French Jesuit school from age 8 to 16; went to Paris at age 17
• Served as army officer
• Settled in Holland in 1628, devoting himself to science and philosophy; used mathematics as a model for his reform of philosophy
• Published in 1637, Discourse on Method
  • Part 2, Optics
  • Part 3, Meteorology
  • Part 4, Geometry (Analytical Geometry, merging of algebra and geometry)
• Published in 1644, Principles of Philosophy
  • Attempt to construct a complete theory of the world out of nothing but concepts of matter and motion
  • In general failed, but made considerable mark in scientific history, particularly Newton
  • Opposed atomic concept, also existence of void
  • Opposed concept of "force field," i.e., action-at-a-distance
  • Proposed long-range force was propagation of impulses through an invisible ethereal matter that he imagined to fill intervening space
  • First to argue that all motion is relative, anticipates Einstein's relativity
  • Proposed vortex theory of motion for planets about Sun; eliminated God from direct action of moving planets or other celestial bodies
  • Inertia is resistance to change in motion not to motion itself
  • Argues bodies possess a "quantity of motion" (modern term is momentum) which they transfer to other bodies by interaction; revision of impetus concept
  • Argues that "quantity of motion" in Universe is finite and remains constant; conservation of momentum
• In 1649 went to Sweden to tutor Queen Christina, died a few months later