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Author Topic: What led Newton to think this?  (Read 4141 times)

blakestyger

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What led Newton to think this?
« on: 26/09/2008 11:52:37 »
Yesterday I went to Woolsthorpe Manor where Isaac Newton was born and where he lived briefly to escape the plague when he was at Cambridge (and where the light-splitting observations were made).

There were demonstrations and displays about gravity, optics etc. The one on pendulums said that Newton thought the Earth was slightly flattened at the poles and he had predicted that a pendulum there would oscillate slightly faster than one at the equator.

Whilst this is now known to be true, the question is: What led Newton to think the Earth was slightly flattened at the poles? Nobody had been there to measure anything and both the geological nature of the Earth and its origin were centuries in the future.



 

Offline DoctorBeaver

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What led Newton to think this?
« Reply #1 on: 26/09/2008 13:47:44 »
Centrifugal force, maybe?
 

Offline syhprum

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What led Newton to think this?
« Reply #2 on: 26/09/2008 16:32:17 »
He may have seen observations of Jupiter where the flattening is quite noticeable.
« Last Edit: 13/01/2009 08:58:40 by syhprum »
 

Offline DoctorBeaver

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What led Newton to think this?
« Reply #3 on: 26/09/2008 17:04:00 »
He may have seen observations of Jupiter were the flattening is quite noticeable.

Good thinking
 

blakestyger

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What led Newton to think this?
« Reply #4 on: 26/09/2008 19:23:01 »
Good point Syphrum - would telescopes then be up to that?
 

Offline RD

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What led Newton to think this?
« Reply #5 on: 26/09/2008 19:40:14 »
Good point Syphrum - would telescopes then be up to that?


I've looked at Jupiter through something with similar magnification to Newton's 6" reflector...




It was clearly evident that Jupiter is oblate, (it was also possible to see Jupiter's red giant spot).

PS
 the sun is also oblate, and can be imaged safely by projecting its image through a low-tech pinhole.
Do not look at the sun either through the pinhole or directly: permanent damage to the retina could result.
« Last Edit: 26/09/2008 19:56:28 by RD »
 

blakestyger

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What led Newton to think this?
« Reply #6 on: 26/09/2008 20:33:55 »
RD, thank you. That may very likely be the answer.
 

Offline yor_on

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What led Newton to think this?
« Reply #7 on: 10/01/2009 23:57:44 »
I looked at it and it seems that what first led him to his conclusion was his theories.

"
In 1679, Newton received a letter from Robert Hooke.   Hooke was asking Newton about the motion of the planets as described by Kepler.  Hooke believed he had figured out a mathematical explanation of why the planets moved the way they did.  Kepler had explained how the planets moved, but couldn’t explain why.  Newton thought about this idea but failed to write Hooke back.  Hooke began to boast that he had solved the problem of planetary motion in 1680.  Newton knew that Hooke’s calculations were wrong but did not want to embarrass Hooke.   

Edmund Halley then visited Newton and asked him about the problem of planetary motion. Newton told Halley that he had already calculated the answer and the effects of gravity on planetary motion. This is known as the inverse-square law. In 1686, Newton would write the book for which he is probably the most famous. Principia included the inverse-square law, the 3 laws of motion, and the Law of Gravitation.

Newton’s Law of Gravitation had many implications.  First, it helped explain the motions of the planets.  Second, it helped explain the curvature of the Earth.  There was a wide debate on where the Earth was flattened and where it was curved.  Many believed that the Earth was flattened at the equator and rounded at the poles.  Many believed just the opposite. 

Newton’s Law of Gravitation implied that the Earth would be flattened at the poles and rounded at the equator.  Rene Descartes believed the opposite.  Jacques Cassini, the son of Giovanni, made measurements that seemed to agree with Descartes.  Later, two other explorers would make journeys towards the equator, which lasted 10 years.  Their measurements backed Newton and proved that the Earth is flattened at the poles.  "

And I believe that those were 'the guys' :)
http://www.saao.ac.za/assa/html/his-exp-arcmeridian.html
« Last Edit: 11/01/2009 00:01:38 by yor_on »
 

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What led Newton to think this?
« Reply #7 on: 10/01/2009 23:57:44 »

 

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