Re: rotation of the earth

Glenn Morton (
Sun, 14 Dec 1997 14:44:58 -0600

At 12:25 PM 12/14/97 -0500, George Murphy wrote:

> This definitely has piqued my interest. The problem, it seems
>to me, can be posed in analogy to a similar paradigm shift, Newtonian
>gravitation to general relativity. In a sense the deflection of
>starlight was the new observation which convinced most physicists of the
>superiority of Einstein's theory. This sort of corresponds to Galileo's
>observation of the phases of Venus, which Ptolemaic theory can't
>reproduce. But Einstein's theory was also strongly supported by the
>excess perihelion precession of Mercury, which had been known for ~50
>years & which Newtonian theory couldn't explain. The anomaly (if indeed
>there is one) resulting from the Magellan voyage would correspond to
>this. But as far as I know it wasn't cited by Copernicus, Galileo &c in
>support of a heliocentric model. & that, even taking intoi account much
>poorer scientific communication in the 16th century, seem very strange
>to me.

If any of this is true, it is an interesting take on history.

> I think we can appeal to continuity in support of my simplified
>argument. Any anomaly seems to vanish if we just take a circular orbit
>of the sun around the earth. Now the eccentricity of the apparent solar
>orbit is small so the necessary solar epicycle is small (unlike those
>for Mars &c) & should not produce a qualitatively different effect from
>the simpler case. But I don't want to be dogmatic, never having done
>celestial mechanics in detail with Ptolemy.

I still don't agree here. The fact that the voyage advances one cycle on
one sphere and retards one cycle in relation to another sphere seems to
present problems to the causality of the ptolemaic system. It is not merely
a reduction to a boat traveling in the direction of rotation of one sphere.
It travels in opposition to the other sphere. Looking at some of Ptolemy's
calculations (I have the Great Books) I think these guys had nothing to do
except calculate. It would have taken a whole lot of work.


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