In the old Aristotelian physics:

• There is a distinction between terrestrial and celestial physics.
• Every terrestrial body has a rightful place and must move naturally toward it.
• The material composition of a terrestrial body determines where that rightful place is.

What should a new "Copernican" physics be like?

• If earth is not the center of the universe, or if there are multiple centers--then what?  How can the natural motion of terrestrial bodies be explained??
• If earth is a celestial body, does it still make sense to distinguish between terrestrial physics and celestial physics?

• no clear guidelines
• more open discussion, argument, and controversy
• more questions about validity of research questions, methods, results and interpretation
• much interest and enthusiasm--a sense of mission

Each star in René Descartes' universe is surrounded by a swirling vortex of matter.  Planets do not possess their own independent motion, but are simply carried around their sun with the rest of the vortex matter.  In this way, Descartes could agree with the general structure of the Copernican system and still argue that the earth does not move relative to its surroundings.

Who was right?
 

René Descartes made many important contributions to mathematics and science.  He derived a mathematical expression to describe the bending (refraction) of light as it travels through different transparent materials.  He introduced the use of exponents to mathematics.  Anyone who has ever plotted points on a graph using an algebraic formula owes Descartes a debt of gratitude.

Perhaps his greatest achievement was his creation of an entirely new method of scientific investigation, a method which he proposed as a replacement for that of the ancients.

Descartes was convinced that humans can gain certain knowledge of the world and how it works, but only if they build that knowledge on a firm foundation of simple and indisputable truths.  Ordinarily, Descartes argued, our minds are cluttered by the distracting and deceptive information that bombards our senses every day.  That is why these simple and indisputable truths have remained inaccessible to our understanding.

Putting his own method to work, Descartes cleared his mind of all preconceptions.  Starting from scratch, he constructed an entirely new system of the world--a world composed only of matter and motion.

The complexity of the observable world is only an illusion, he claimed.  In reality, everything we humans sense is the product of innumerable collisions between extremely small particles of matter.  These collisions are controlled by two basic ideas:

• The total quantity of motion in the universe is always constant.

• Collisions are like contests whose outcomes are determined by the size and velocity of the contestants.

Huyghens did not share Descartes' extreme skepticism about the value of experimental results.  Human senses may be faulty, he admitted, but they are not totally unreliable. 

With adequate care and repetition of controlled scenarios, Huyghens was confident the limitations inherent in human sensory perception could be reduced.  He knew from experience that human senses could be artificially extended through the use of instruments.

At the age of 26, Huyghens designed and built an excellent telescope with which he discovered the ring of Saturn as well as its moon Titan, the first moon of that planet to be identified.  At the age of 27, he designed and built an accurate clock.  By introducing this new instrument into the investigator's toolkit, Huyghens revolutionized the study of moving bodies.  His pendulum-driven timepiece allowed him to make more precise measures in free-fall experiments than any of his predecessors.

For Huyghens, using experimentation hand-in-hand with reason proved a winning combination throughout his life.  His methodical study of colliding bodies led him to reject Descartes' ideas on collision and propose a very different set of rules governing their behavior.

They will be reflected and continue to move at equal speeds.

They will be reflected and continue to move at equal speeds.

The slower one will be reflected.  Both bodies will continue to move in the direction of the faster one with a speed that is the average of the two.

They will move with their speeds reciprocally exchanged.

The moving body will give some of its speed to the one at rest, and will be reflected back with the larger share of that speed.

The moving body will stop while the one that had been at rest will move forward with the same speed as the body which struck it.

No matter how fast the moving body is going, the body at rest will not be moved at all while the one in motion will be reflected.

No matter how slowly the moving body is going, the body at rest will be moved.

A calculus fit to compute on,
White light, and a head to drop fruit on,
A mind to absorb it,
And soar into orbit--
That's all that it takes to be Newton.

Nature and Nature's laws lay hid in night:
God said, "Let Newton be!" and all was light.

       --Alexander Pope (1688-1744)

• The rays of the sun.
• Comets.
• Falling stars.
• Rainbows, haloes, sun pillars, etc.
• Lightning.
• Eruptions of flames from the cavities of mountains.
• Flame of every kind.
• Natural hot springs.
• Damp hot weather at any time of the year.
• All shaggy substances (wool, animal skins, feathers).
• All bodies placed near fire for any time.
• Sparks arising from striking flint against steel.
• All bodies rubbed violently.
• Iron, when first dissolved by acids in a glass.
• The bodies of animals (except insects).
• Horse dung, and other animal excrement, when fresh.
• Strong sulfuric acid will burn a hole in a piece of fabric.
• Alcohol burns the mouth.
• Some plants are warm to the tongue and have an almost burning taste when chewed.
• Strong vinegar and all acids cause a pain almost like that produced by heat when they come into contact with any part of the body not covered by skin.
• Severe and intense cold produces a sensation of burning.