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Very interesting and true comments, Alexandre, especially with regard to
the fact that "only the people who made the very last step in certain
inventions are recognized and remembered, no matter how relatively small
their contribution could be. The real giants, to whom we owe
most of our knowledge, tend to be forgotten."

Consider Hypatia of Alexandria (?350/379AD to 415AD) and her role in the
invention of the planispheric astrolabe.  As Hoskin (1997) states, the
most historically important astronomical and navigational instrument of
the Middle Ages was the Astrolabe.  It survived as an astronomical &
navigational instrument for over 1000 years.

Most references agree that the actual origin (and inventor) of the
astrolabe is shrouded in mystery.  Ptolemy certainly discusses the
principles of stereographic projection 200 years earlier. What is known,
however, is that the earliest surviving astrolabe treatise was compiled
by Theon in the 4th Century.  Theon's daughter was Hypatia.  Theon's own
handwritten words, which are contained in the preface of his comentary
state that 'the edition having been prepared by the philosopher, my
daughter Hypatia".

In Ptolemy's time, the main instrument usede to calculate astronomical
positions was the armillary sphere, which was large and cumbersome, not
lending itself to everyday use.  Ah, so there was a need for a more
refined practical instrument!  Did Ptolemy ever build one?  I have found
no record, or direct evidence of this, although he had certainly
calculated the mathematics and geometry, at least in principle.

Enter Hypatia and Theon.  In Synesius' letter to Paeonius (letter 154),
he refers to another work De Dono Astrolabii, in which he claims that he
himself designed an astrolabe as a gift to an acquaintance, but he
acknowledges he need Hypatia's help to do this.

As Michael Deakin from Monash University (History of Mathematics - The
Astrolabe) states, this letter is seen as an important document in the
history of astronomy and navigation.

Well, that's my 2 cents worth!

Lisa

Alexandre Eremenko wrote:
> 1. Contrary to some messages on this list,
> the moon eclipse will occur not "tonight" but
> TOMORROW night. That is on October 27 for most
> of the US and at small hours October 28 in Europe.
>
> 2. I want to use this opportunity to pay tribute to some
> people whose efforts made the very business of
> Cel Nav possible at all,
> and
> who are rarely mentioned on this list.
>
> The idea of using Moon eclipses to find longitude
> is credited to
> HIPPARCHUS, who probably was the greatest astronomer
> of all times, and possibly, one of the greatest mathematicians.
> He lived in II century BC.
> We know almost nothing about his life,
> and none of his original writing survives.
> Ptolemy calls him "a hard-working man, and an admirer of Truth".
>
> Most of our knowledge about him
> comes from the references in the books of Ptolemy,
> but Ptolemy was writing
> 300 years after Hypparchus.
>
> (The time span is like the time span between Newton and us!)
>
> Hypparchus own astronomical observations, referred by
> Ptolemy permit to establish the time when Hipparchus lived,
> by applying the Lunar theory of Hipparchus backwards in time:-)
>
> (So he built a good memorial for himself, did not he?:-)
>
> 90% of our knowledge about Moon motion was known to Hypparchus.
> (part of it is apparently due to "Chaldeans" of whom we know
> nothing).
>
> Most of this theory was derived by Hypparchus by careful
> reduction of the eclipse observations of Chaldeans and of
> hismelf.
>
> The method of finding longitude by the eclipses of the Moon
> (and Sun) remained the ONLY method of finding longitude for
> almost 20 centuries!
>
> This was the only method Columbus could use.
> (Though he was not very successfull with this,
> due to the general collapse of knowledge and educcation,
> which came soon after
> Ptolemy and lasted for about 1500 years).
> This was also the only practiceable method on land,
> to make geographic maps. (The direct measurements of distances
> on land was VERY imprecise).
>
> Hipparchus theory of the Moon motion was not superceeded
> until Tycho Brahe (XVI cent AD), who added a correction term
> of 40' amplitude.
> Neither Copernicus, nor Kepler added much to the Lunar theory
> in the sense of prediction of the Moon motion.
>
> Only due to Newton's mechanics further improvements became
> possible. However, Newton himself failed to explain the
> known irregulatities in the Moon motion. He could not
> overcome the mathematical difficulties. The whole gravitation
> theory was seriously questioned because of this faillure.
>
> It is only due to the efforts of the great Euler and Claiaut that
> approximately in 1750-s the Moon motion was shown to
> be consistent with and explainable by the Newton mechanics.
> (Euler was found eligible for 300 pounds of the Longitude Prize,
> and Meyer who actually developed the tables based on Euler's
> theory got 3000 pounds. More precisely, these 3000 pounds were
> delivered to Meyer's widow:-(
>
> 3. This story confirms the sad truth that only the people who
> made the very last step in certain invention are recognized and
> remembered, no matter how relatively small
> their contribution could be. The real giants, to whom we owe
> most of our knowledge, tend to be forgotten.
> This tendency in increasing in our time, with general
> decline of interest to history, and I afraid, to science itself.
> For example Norie (1828) mentions people like Hipparchus,
> Mercator and Newton (and Newton is always endowed with an epitet
> like "immortal". You won't find this in the modern version of
> Bowdich:-)
>
> Alex.
>
>


--
Kind regards
Lisa Fiene
***************************

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