Re: rotation of the earth

Glenn Morton (
Wed, 17 Dec 1997 19:35:42 -0600

Hi Don.

I know I said that Magellan was dead but he seems to keep escaping his
coffin and walking the earth. He, his voyage and Manchester are not high on
my popularity list right now. :-) But there are a couple of things that I
probably need to respond to in your post. First, I want to note that this
whole thing started from believing Manchester who is a well respected
historian (although he is dropping on my list at the moment). And I want to
note that this thing is so peripheral to the issues that I find most
fascinating (early Genesis and Science) that I am not inclined to defend
this very vigorously. I made mention in my first book, Foundation Fall and
Flood, of this as an example of Christians forcing a choice between what you
see and what theology says. I really don't need this example to illustrate
that issue and can replace that illustration with thousands of other equally
(or more) valid illustrations of Chrsitians choosing to believe their
personal interpretation of scripture rather than what their eyes tell them.
Anyway to the comments.

At 04:08 PM 12/17/97 -0700, Don N Page wrote:

> So I think Glenn is right that the situation is complicated, and there
>are many sorts of time measures the crew could have gotten with various
>measurements they might have made. If they had compared enough of them, they
>could presumably have found a discrepancy with their apparent implicit
>assumption that they were at fixed longitude (i.e., in using their local solar
>time as a measure of the total passage of time).
I very much appreciate you taking the time to look at the complexity of the
Ptolemaic system. I really don't think most modern peoples appreciate that
complexity nor see the many places one MIGHT get (I don't know yet)
contradictory evidence from Magellan's voyage.

> However, I would emphasize two points on this:

> (2) From what Glenn and others have told me so far, there doesn't seem
>to be evidence that the voyagers tried to measure time by the angles between
>objects purely in the heavens, as they did not remark on noticing any
>discrepancy with their local solar time (by the implicit fixed-longitude
>assumption) until they compared notes with the islanders.

I don't know what measurments they might have made since Manchester does
such an abysmal job of documenting where he got the info. As I noted he has
a big bibliography but no footnotes so I am not going to be able to read
everything he read to find the facts I want.

> Another point I am curious about is Glenn's claim that Ptolemy's system
>would have predicted that the moon, if of fixed physical size, would have an
>angular size that varied by 100% during the month. Why didn't Ptolemy's
>have the moon going round the earth on a circle that was eccentric by an
>proportional to the eccentricity of its Keplerian orbit? I would have guessed
>that the latter were used, and that then the error would be only quadratic in
>the eccentricity and hence probably unmeasurable. In fact, I am also curious
>as to how early one could measure the actual angular size variations in the
>and moon between apogee and perigee.

This is NOT my claim (I am merely the messenger) but the claim of A.C.
Crombie (verified by Ted). Crombie claims "It was left for Nicholas
Copernicus (1473-1543) to elaborate a system which could replace Ptolemy's
as a calculating device and yet represent physical 'fact,' and also 'save'
additional phenomena, such as the diameter of the moon, which according to
Ptolemy's system should have undergone monthy variations of nearly a hundred
per cent." Medieval and Early Modern Science Vol 2, 1959, p. 167
> Glenn, if you know of some observation that the voyagers made that was
>clearly in conflict with Ptolemy's system even when one puts in the fact that
>the voyagers were observing from different positions on a round earth, I would
>be curious as to what it is and how you calculated the discrepancy.

As I noted I don't have any calculations that the crew did. (And once
again, I am finding this frustrating because I am not claiming that I did).
I pointed out that a trip around the world in the Ptolemaic system leads to
what I would view as problems of causality (or transmission of motion
problems) in the Ptolemaic system. The galilean transforms I posted a
couple of days ago show that the trip causes you to lose one revolution with
respect to the stellar sphere but gain one on the other spheres. Since the
ratios were important in that system, if you believed that the system was
real, you would have a causality problem. It may be as Ted suggests that
they didn't view Ptolemy as real.

I think I have been convinced to replace the Magellan example as simply too
big of a head ache. I can find plenty of other examples of christians who
would rather believe their ability to interpret the Bible than what their
eyes see. I will find a simpler one and there will be no more defence or
interest in this issue for me.

Now, Magellan, back in your coffin!


Adam, Apes, and Anthropology: Finding the Soul of Fossil Man


Foundation, Fall and Flood