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Re: Early lunars
From: John Huth
Date: 2010 Mar 20, 07:52 -0400
George -
From: John Huth
Date: 2010 Mar 20, 07:52 -0400
John Kirtland Wright does not definitively say that some form of lunars were employed to find the longitude of major cities, but advances the conjecture with some evidence, particularly citing Roger of Hereford's observation of lunar eclipses. I'll just quote the text here from the "Notes on.." paper:
"Though these various method were known to astronomers and astrologers, there is nothing to show that any large number of positions were determined by astronomical means. We know, however, that between the twelfth and fourteenth centuries, tables were constructed for the meridians of at least a dozen cities; we have in manuscript such tables for Toledo, Marseilles, Hereford, London, Toulouse, Cremona, and Novara, and we have clear evidence that similar tables were in existence in 1232 for Paris, Palermo, Pisa, Constantinople and Genoa.
In their construction some sort of astronomic observations must have been made and it is more than likely that the eclipse method of finding longitudes was given practical application. that this was done in the case of tables for Hereford, Marseilles, and Toledo is certain, for Roger of Hereford, who adapted the Toledo Tables to the meridian of his city, tells us that the time of the eclipse of September 12th, 1178, was observed in these three cities and that their longitudes in relation to Arin, the world center, were in that way determined. It will also become evident from what follows that the relative positions of several other points in Europe were known with sufficient accuracy to warrant us in concluding that the differences in longitudes separating these points had been calculated by astronomical means."
Pages 84 and 85 in Wright's paper.
I omitted the references in the above. "Arin" was a mythical city that was used to denote the halfway point from the prime meridian used during that era. It was a tool to aid the calculations more than anything else, according to Wright's paper.
The other observations that I'm aware of were two measurements of longitude carried out by Columbus during two of his voyages. He carried with him ephemerides constructed in Nuremberg (I forget the name of the astrologer who constructed them). In both cases he timed the lunar eclipses against the time of sunset. Unfortunately, the values he derived were quite far off. This I obtained from Samuel Eliot Morrison's biography of Columbus. One of the measurements was of St. Ann's Bay in what is now Jamaica, where, incidentally, he obtained a latitude using a quadrant on Polaris of 18 degrees, 30 minutes, which is phenomenally good for a quadrant sighting the North star (having tried this myself in Jamaica). I should add that in both measurements, he was on solid ground, not on shipboard.
Best,
John H.
On Sat, Mar 20, 2010 at 7:01 AM, George Huxtable <george@hux.me.uk> wrote:
Thanks for the information, and the offer of a scan.
But there's no urgency, just interest. Isis is available to me, both in the
library of the Museum for the History of Science, in Oxford, and in the
Bodleian. I'll add it to my long list of things to look at, next visit.
If there's evidence of any real astronomical determination of longitudes,
before 1500 (or even before the early 1600s), I would be interested to
learn about it.
Ptolemy's Geographica arrived back in the West some time after 1400. We
discussed the Marseilles tables on the list a few months back, and as I
remember, these were stated as dating from 12th century, well before that
recall of Geographia, and contained many longitudes, some good ones and
some very bad ones. I have presumed these came from dead-reckoning of
travellers, in day's journeys, by land or sea, rather than by astronomy. Is
that wrong?
George.
contact George Huxtable, at george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
----- Original Message -----
From: "Apache Runner" <apacherunner@gmail.com>
To: <NavList@fer3.com>
Sent: Saturday, March 20, 2010 9:52 AM
Subject: [NavList] Re: AW: Early lunars
Wolfgang -
Yes on both accounts.
John H.
On Sat, Mar 20, 2010 at 5:30 AM, Wolfgang Köberer <
koeberer@navigationsgeschichte.de> wrote:
> This is the article, I presume:
>
> Wright, John Kirtland
> Notes on the knowledge of latitudes and longitudes in the Middle Ages.
> in: Isis, Vol. 5 (1923), 75 - 98.
>
> He has also written a book on "The geographical lore of the Time of the
> Crusades".
>
> I can bring along a copy of the article in May, George, or send a scan.
>
> Wolfgang
>
>
>
>
>
