# B Ways to prove Newton's theory in the early days

1. Dec 3, 2017

### Tio Barnabe

I was thinking about the immediate ways that physicists had for checking the validity of Newton's theory of gravitation in the time Newton published it. An obvious way would be to check if it predicts what is stated by Kepler's laws. Does anyone know if this was made? Do you know of other tests they carried out?

BTW, I found this text http://radio.astro.gla.ac.uk/a1dynamics/ellproof.pdf showing that the theory "predicts Kepler first law", but it seems to be too complicated for being worked out at that time.

2. Dec 3, 2017

### phyzguy

Newton's Principia, published in 1687, has a detailed derivation of how Kepler's three laws can be derived from his laws of motion and his law of Universal gravitation.

3. Dec 4, 2017

### vanhees71

Yes, and this was the main motivation for Halley to push Newton to publish his most important work. The funny story is that Halley once asked Newton, how to explain Kepler's laws from physics. Newton answered that this follows simply from the $1/r^2$ law for gravitational forces, and Halley had a hard time to make Newton write up the derivation. Apparently Newton considered his alchemistic work much more important than the ground-breaking physics work we nowadays associate with his name.

4. Dec 4, 2017

### Dr.D

Most folks would agree if they thought they were on the verge of a break-through to make gold from lead!

5. Dec 7, 2017

### Mister T

Some historians have argued that his exposure to mercury during his alchemy experiments had poisoned him. That could distort your sense of what's important!