[ISHMap-List] list serve message re: bicentenary Rizzi Zannoni

Douglas Sims dougsims1945 at yahoo.com
Sun Jan 19 20:54:01 CET 2014

Dear Vladimir Bulatov.  Good to hear your voice, and good to know that we are on the list together!.  Thank you for your response.  It was nicely described, and it is a start.  But I'm afraid it does not answer the question.  The method you describe is that often described by the ancient geographers.  It is effective, of course, but it is very approximate.  Precisely the point I wished to make (but evidently failed to do so) was that, such methods (the gnomon and shadow; the equal altitudes, etc., all close cousins), while useful in a school-book sort of way, could not possibly provide the accuracy needed to find latitudes OR longitudes (for the question is germane to both) with much precision.  What I'm looking for (and which may not exist!) is a method that would provide greater precision than these methods, or perhaps a procedure which would refine those methods to the point that they really become useful.  What few comments I have seen on
 the subject are disappointing, saying nothing to the point, but use the ancient method of gobbledygook (spelling?), that is, simply facile run-downs of esoteric terminology.

Vladimir, what you say about using the line to obtain latitude is true of course, but it is only the most obvious of several usages.  As you know, up until the late 18th century, approximately, astronomy was virtually entirely "positional astronomy", and very many used the term 
"meridional astronomy", for it was precisely by usage of an overhead marked meridian that the sundry positions of places were best found. They timed the passage of stars over the meridian for the right ascension (longitude on the celestial sphere [oddly, not the same thing as celestial longitude]), and took their altitudes on the same meridian at the moment of crossing to obtain declination (latitude on the celestial sphere [oddly, not the same thing as celestial latitude]).  Thus a reliable set of locational coordinates was obtained.  These were the important things needed to plug into the Cosine Theorem in order to get the time difference between two meridians, which combined with other factors, gave one (at last!) the local terrestrial longitude.  So you can see that the line was vital in the long run to accurate longitude finding as well as latitude finding.

A simpler example is obtaining terrestrial longitudes by culmination of the moon.  This culmination refers (as you no doubt are aware) to the moment the moon (its center) crosses the meridians in two places, the longitudinal difference between which it is wished to know.

There are many other connections between finding latitude and longitude coordinates and establishing one's meridian.  Thus the importance of how these fellows found these all important lines.  The question remains open, for I think that these simple old methods would not suffice for much precision.  Certainly my expertise is limited here, as my question proves.  But my curiosity remains, and I do not lose hope for some clear, comprehensible answers which go straight to the point.  Sometimes I think that perhaps the old geographers did indeed simply use a primitive method, and that the only refinement to the procedure was just to follow the procedure with the greatest possible he could, and that in fact no other course existed which one could follow.  But I am not convinced.

I see that there are now several other responses waiting to be read, so I shall bid thee fare for now, and get to them. 


Douglas W Sims
3516A Bayview Av., apt F
Brooklyn, NY 11224

On Sunday, January 19, 2014 6:05 AM, Владимир Булатов <v.bulatov at mail.ru> wrote:
Dear Doug,

Of course I am not sure about the procedure used by Zannoni, but I can describe the method used by Russian geodesists in his time.
Determination of the meridian line took the whole sunny day, but was rather simple. A geodesist used a long vertical pole and a rope. In the morning he marked the shadow of the pole and with his rope drew a circle around the pole with a radius equal to the length of the shadow. In the evening, when the shadow touched the sircle, he marked its new position also. The meridian line made the bissectriss between the two shadows.
But this pocedure has nothing to do with determination of a longitude, it was but a first step to determine the latitude.

Sincerely Yours,

Суббота, 18 января 2014, 14:55 -08:00 от Douglas Sims <dougsims1945 at yahoo.com>:
January 18, 2014

Dear ISHMappers, Mary, and Vladimir,

Concerning the January 24 erecting of a plaque to indicate the spot where Rizzi-Zannoni established his meridian line:  Is it planned to publish any papers in connection with this, especially anything telling us what procedure(s) Rizzi-Zannoni used in obtaining his meridian line?  As implied by Vladiniro, certainly he could not hope to establish a longitude difference between his point and any others with much accuracy without a reliably marked meridian for his location.  Thus, there was incalculable importance in the job of getting this line as accurately as possible.

In my experience, the question of establishing a meridian line is treated in our literature rather like the question of the determination of mean solar time, both essential to finding longitude differences..  Both are often treated as somewhat taken for granted, and it is assumed without a second thought that some simple and certain procedure exists.

Actually, as some ISHMappers will know, they are excruciatingly difficult things.  As to the meridian line, obviously, one could not have simply used a compass.  Far too shaky, and, besides, though the existence of magnetic declination was recognized, it was far from being understood.  As far as I know, the method usually used  was some sort of equal-altitudes maneuver.  But here too, since the earth is spinning constantly, and human beings tend to slightly quake, one is much limited in obtaining the necessary degree of accuracy in the instantaneous altitudes that he takes, and assuring that they are taken exactly at the right instant.

A good indication of the tremendous difficulty of this is the simple fact that almost no one, among the old geographers and astronomers consulted by me (a good number), ever explains the method that he used.  This, although the finding of this line as accurately as possible is essential to not just map-making, but also to other things, such as founding observatories, compiling ephemerides, themselves also in the end essential to accurate map-making.

This is a silence which speaks loudly to me.  The impression I receive is that our scholars usually simply pass over this all-important thing in silence, apprehensive that he will come under criticism for taking insufficient pains if he describes the procedure used in detail.  He feels, I suspect, that virtually all readers will fail to notice the omission, an omission oddly just as unnoticeable as it is enormous.  To the matter of increasing coordinate accuracy over the centuries, certainly we have here the germs of a virtually unexplored, but vital, element.

I have devoted much time to this question, and shall again as soon as other exigencies allow it.  Thus my great interest in finding out if, during the Rizzi-Zannoni commemorative activities, there will be any publications released, in particular in connection with the question of exactly what method(s) Rizzi-Zannoni used in finding his line.

Thank you,

Doug Sims

Douglas W Sims
3516A Bayview Avenue, apt. F
Brooklyn, New York, 11224

On Saturday, January 18, 2014 10:06 AM, Mary Pedley <mpedley at umich.edu> wrote:
Dear colleagues: 

Please find the attached announcement from Vladimiro Valerio regarding the opening celebrations of the bicentenary of the death of geographer and cartographer Giovanni Antonio Rizzi-Zannoni

On the 24th of January a plaque will be placed at the Castel Sant'Elmo in Naples, Italy, to mark the spot used by Rizzi-Zannoni to establish the meridian line and center of the coordinates for his new map of the Kingdom of Naples (1787-1812). The ceremony at Castel Sant'Elmo will inaugurate a year of celebratory activities honoring the Italian geographer with renewed study of his life and works. 

Thank you. 

Mary Pedley 


Mary Pedley
Map Division 
William L. Clements Library
The University of Michigan 

Temporary address:
1580 E. Ellsworth Rd.
Ann Arbor, MI 48108

 909 S. University Ave
 Ann Arbor, MI 48109-1190
 734-764-2347 voice
 734-647-0716 fax

ISHM mailing list
ISHM at lazarus.elte.hu

ISHM mailing list
ISHM at lazarus.elte.hu


Владимир Булатов
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lazarus.elte.hu/pipermail/ishm/attachments/20140119/fafbcf62/attachment.html>

More information about the ISHM mailing list