Announcements Next exam is scheduled for Thursday March 24. Will cover Chapters 6 & 7 and possibly some of Chapter 8. Sample questions will be posted this week. Dark Sky Observing Nights next week on Monday and Wednesday. Forecast doesn’t look good for either or the alternate day on Thursday. If we go, set-up starts at 6:30pm. If needed, I’ll post a cancellation notice on APSU Astronomy by 5:00pm on the day of the observing.

In 1660 the Greshamites form the Royal Society The Philosophical Transactions of the Royal Society have been published since 1665 and are available online

Robert Hooke is the Curator of Experiments for the Royal Society Known as London’s Leonardo because of his involvement in the rebuilding of London after the great fire of His experiments on the pendulum gave rise to Hooke’s Law. Check out the official Robert Hooke website

Hooke postulates an attractive force between the Sun and planets that diminishes with distance He never showed it was an inverse square law, just an inverse law of some sort.

In a series of letters, Hooke spurred Newton into thinking about Gravity Hooke’s “discussions” with Newton became somewhat critical of Newton’s ideas. As a result, Newton despised Hooke and eventually tries to erase all traces of him from the Royal Society records

Isaac Newton 1642 – 1727 Born at Woolsthorpe Manor in Lincolnshire three months after his father dies. He is raised by his maternal grandmother after his mother remarries. He isn’t nobility but he does have status above the peasantry

Early on, his mother wants him to run the farm Isaac absolutely hates farming and openly shows his dislike of it Fortunately, the local school master convinces Isaac’s mother to send him back to school. Eventually, he enters Trinity College at Cambridge in 1661.

In 1665 Plague hits London and Newton goes home to Woolsthorpe While at home he continues his studies on his own. It is during these two year that he forms his early ideas about light, motion, gravity and the foundations of calculus. He is still very much a Cartesian at this time but he is beginning to question it.

In 1669 Newton is appointed the Lucasian Chair of Mathematics at Trinity College in Cambridge The chair is currently held by Steven Hawking

Due to an early “run-in” with Hooke over the behavior of light, Newton becomes a recluse at Cambridge

By 1684 Hooke, Wren and Halley are in discussions on the nature of the force binding the solar system

Edmund Halley decides to visit Newton and asks about orbits

After Newton sends Halley a 9 page proof that the orbits are ellipses, Halley starts pushing Newton to publish his work

Newton’s first draft contained his 1 st Law of motion and an inverse square law of gravity He still had not figured out his 3 rd Law and his law of gravity was a little fuzzy with only an inverse square distance relationship

His second draft brought him to his 3 rd Law and the mutual nature of the force of gravity He immediately saw the problem that it would be impossible to calculate precisely the orbit of any planet with all the other planets and the Sun pulling on every other object

His biggest hurtle was determining the force of gravity of an extended object It is this problem that leads him to the invention of calculus

He proved the universality of his law of gravity by comparing the fall of an apple to the “fall” of the moon

His next proof was to explain the complicated lunar orbit

Newton is also able to derive all three of Kepler’s Laws

Just before he was ready to publish, Hooke tried to interject himself As a result, Newton makes much of his work overly mathematically complicated, beyond anything Hooke could understand Halley must do a great deal of soothing to calm Newton down and convince him to complete the work

Finally, Principia is published in July 1687 It is an exceedingly difficult book to read with lots of overly complicated math. It is not a book that could be used to teach others physics. A 2 nd Edition is published in 1713 and a 3 rd Edition is published in 1726

Thanks to Samuel Clarke’s edition of Jacques Rohault’s Treatise of Physics an understandable bit of Newtonianism came out

Once others got into the act, more proofs of universal gravity and Newton’s laws came about The Paris Academy of Science attempted to decide between the shape of the Earth as predicted by Descartes and that predicted by Newton using the lengths of pendulums. Their results were inconclusive

The most triumphant proof was by Edmund Halley and his prediction of the return of his comet Halley noted the orbits of the comets of 1682, 1607 and 1531 were all very similar. His calculations show they are all one object and he predicts it will return in 1758

Halley’s prediction was improved by Alexis-Claude Clairaut The problem was the perturbing influence of Jupiter. Clairaut’s prediction was only a month off in perihelion

The biggest problem with universal gravitation was the 3-body problem

Many of the most famous mathematicians of the 18 th and 19 th Centuries worked on the problem Joseph Lagrange Leonhard Euler Simon de Laplace Jean D’Alembert

After the publication of Principia, Newton moves on He serves as Master of the Mint from 1699 for almost 30 years until his death in 1727

He is knighted by Queen Anne in 1705 He also serves two unremarkable term in Parliament as the member from Cambridge 1689 – 1690 and

Newton dies on March 20, 1727 He is buried in Westminster Abby