Newton

Kevin T. Kelly

Department of Philosophy

Carnegie Mellon University


In 11th and 12th centuries the population expanded, leading to new towns. Newton = new town.

Isaac Born in Lincolnshire countryside, Christmas Day 1642, same day as Galileo died.

Newtons illiterate, but rising economically for a century.

Grandfather bough Woolsthorpe manor.

Mother from Ayscough family, socially declining gentlemen.

Father died three months before Isaac's (premature) birth.

At 3 yrs, new elderly stepfather Clergyman Smith (M.A. at Oxford). Smith brought his library to Woolsthorpe. Isaac left with grandmother.

At 11, Smith dies.

At 13, Latin gammar school at Gratham. Models, measures storm strength by jumping in opposite directions. Found equinoxes by plotting light on the wall.

At 17, called back to manage Woolsthorpe. Failure.

At 18, Uncle Ayscough and schoolmaster urge on his education.

At 19, matriculates at Triity college, Cambridge. Degree mill with irrelevant aristotelian curriculum. Gentlemen obtained Anglican church posts without finishing.

Subsizar status: servant of other students. Only sizars were serious students.

At 22, Philosophical questions: notes on Descartes, Gassendi, Galileo, Boyle, Hobbes, Digby, Galanville, More, Keplerism. Stir about Descartes at the time. Designed windmills to get power out of the vortex of the heavens. Sharp critique of theory of light as pressure. Looked at sun and stuck a knife behind his eye to see spots. Encountered Kepler's astronomy, discovered that white light is composed of colors.

Newton leaned toward Gassendi's atomism in optics and gravitation. More's platonism raised concerns about mechanical philosophy that affected Newton.

Read Schooten's Miscellanies, Descartes Geometry, Wallis. Heard lectures by new Lucasian Math Professor Isaac Barrow (rare opportunity). Skipped Euclid and regretted it later.

At 23, Final exam with Barrow, who was not impressed by his ignorance of Euclid, but passed him. His experience of learning analytic geometry and algebra before plane geometry was unique.

By 24, Infinite series, area of hyperbola, binomial theorem, fundamental theorem of calculus.

At 24: Plague forces him back to Woolthorpe.

Waste book:

Physics: rejects Descartes' laws of impact. Works on concept of force, starting from an impetus perspective and an inertia idea.

"force of motion" like our momentum. Discovered equal and opposite reaction by thinking of reference frame of center of gravity of the two bodies.

Derives "centrifugal" force law for uniform circular motion v^2/r in terms of impacts aroung regular polygons inscribed in a circle. Independently obtained by Christiaan Huygens.

Reads Galileo's problem of calculating fall of objects to keep them on Earth's surface using radius of Earth r and length of day to get v. Checks against acceleration of gravity using the same rule and a 45 degree conical pendulum. Galileo was off by a factor of two.

Later, he applied the formula to the moon to calculate the force holding it in its orbit. The ratio of force at the Earth's surface to that at the surface of the moon was 4000:1

Then he substituted in Kepler's 3rd law and found an inverse square relation of centrifugal force according to distance from the sun. Halley would independently discover this later. By inverse square gravitaion and a lunar orbit of 60 earth radii, the ratio should be 3600:1. This is the calculation that "answered pretty nearly".

At this time, he thought circular motion was equilibrium between centrifugal force and attractive force and sided with impetus over intertia.

Apple story was a way to give him priortiy over Huyghens.

Optics: Read Boyle, Descartes, and Hooke's Micrographia on light. Investigated on his own.

Hooke said that colors were "tearing" of wave pulse. Newton rejects this because sound waves spread and light doesn't.

Experimented with manufacture of hyperbolic lenses to correct sphereical aberration. Realized that chromatic aberration can't be corrected.

Newton's rings phenomenon. Uses circular acceleration formula to calculate thickness of air gap at ring positions!

At 26: Fellow at Trinity college. Takes up alchemy,

"When Newton lectured, so few went to hear Him and fewer yet understood him that oftimes he did in a manner, for want of Hearers, read to the walls".

More optics:

Managed to reconstitute white light out of the spectrum, concluding that white light is composed of particles of different colors.

Reflecting telescope to eliminate chromatic aberration. Causes sensation at Royal Society where Hooke is on staff as experimental technician.

At 30: submits paper on colors to Royal Society. Hooke claimed to have done the experiments and know better.

At 37: total withdrawal from physical correspondence.

More work on alchemy. magic, spirit, occult. Thinking on gravitation influenced by More. Licked heavy metals and experimented with antimony.

Lots of theological work. Reconstruced a plan of the Jewish temple.

Hooke sends a note about planetary motion being composed of centripetal force and tangential motion (genuine modern approach). Asks how a rock would fall through the surface of the earth.

Newton botches the answer with a spiral to the center. Hooke says it would be a spiralling ellipse. Calcluation is a mess.

Defining moment! Newton got to work and replied with a precessing ellipse and started calculating the orbital path.

Demonstration of law of areas

Demonstration of inverse square variation of force araound ellipse.

Profound change in his thinking based on Alchemy, More, and Hooke's note.

Comet observation through telescopes.

At 42: Halley's famous visit, beginning of Principia Mathematica.

Newton's father was an illiterate farmer