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The Leardo Map of the World, 1452 or 1453: In the Collections of the American Geographical Society — John Shaqi

The Leardo Map of the World, 1452 or 1453: In the Collections of the American Geographical SocietyWright, John Kirtland

History

The Leardo Map of the World, 1452 or 1453: In the Collections of the American Geographical Society

Name: The Leardo Map of the World, 1452 or 1453: In the Collections of the American Geographical Society
Author: Wright, John Kirtland

Wright, John Kirtland

Early maps; Leardo, Giovanni

[9]Grotefend, _op. cit._, p. 113, asserts that O was usually omitted to
    avoid confusion with zero. Leardo, however, includes O. J and I are
    counted as one letter. The golden number of 1453 is 10; Leardo’s A
    corresponds with golden number 8.

[10]The following is a comparison of the times of the new moon on
    certain dates as indicated by Leardo with the actual times as
    determined for the meridian of Venice from Th. von Oppolzer, _Canon
    der Finsternisse_ (constituting _Denkschr. Kaiserl. Akad. der Wiss.
    in Wien, Math.-naturw. Classe_, Vol. 52, 1887).

                 Leardo’s Times                     Actual Times

      1453    Dec. 1     ? hrs.  203? pts.     Nov. 30     2.40 P. M.
      1455    Apr. 16   21 hrs.      ?         Apr. 17    12.22 A. M.
      1456    Apr. 6     7 hrs.   229 pts.     Apr. 5      4.25 A. M.
      1461    Jan. 11   21 hrs.      ?         Jan. 11     8.44 P. M.
      1468    Feb. 23   14 hrs.   747 pts.     Feb. 23    10.15 P. M.

    The discrepancies are too great and too variable to enable us to
    come to any very definite conclusions as to the place or manner of
    origin of Leardo’s figures.

[11]The division of the hour into 1080 points (3×6×60, as Dom Bévenot
    points out) is puzzling. More usually the hour was subdivided into
    four points. See Grotefend, _op. cit._, p. 188.

[12]The dominical letter for 1453 was G.

[13]On the basis of certain of the figures given by Leardo for the
    lengths of the days at about the times of the solstices, I have
    estimated that this table was worked out for about lat. 42° 45′ N,
    which is more nearly the latitude of Orvieto than that of Venice
    (45° 30′). (This calculation was made with the _Smithsonian
    Meteorological Tables_, 4th edit. (constituting _Smithsonian Misc.
    Colls._, Vol. 69, No. 1), Washington, 1918: Table 87, “Duration of
    Sunshine at Different Latitudes,” and Table 88, “Declination of the
    Sun for the Year 1899.” The difference in the declination of the sun
    for 1452 and 1899 is negligible.) Dom Bévenot writes: “I fancy day
    lengths were reckoned roughly for degrees. Here in Weingarten about
    1490 they used tables drawn up for lat. 45° N, though the place is
    actually 47° 40′.”

[14]I am indebted to Dom Bévenot for the following comment:

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The Leardo Map of the World, 1452 or 1453: In the Collections of the American Geographical Society

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