The Southwestern Historical Quarterly, Volume 29, July 1925 - April, 1926 Page: 81
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Early Art of Terrestrial Measurement and Its Practice 81
lowers of the Faithful and their generals to know in which direc-
tion, and how far away, lay Mecca. But these measurements
required an expertness not commonly possessed by the explorers of
the Spanish Main.
During the age of discovery the Spanish universities led the
world in teaching the science of astronomy. Yet writers on the
subject advised practical navigators not to occupy themselves with
the vagaries of longitude; but, to adhere to the method of latitude
determined by sun's altitude, and to check the ship's position by
the method of "dead reckoning."
To perform this nautical operation the mariner charted his
course hourly by platting the ship's direction, read from the com-
pass, and the distance sailed from log measurements. A log, with
rope attached, was thrown overboard. The rope was paid out and al-
lowed to run freely for such length of time as it took a sand glass to
empty itself, usually about one minute. Then by ascertaining the
amount of rope paid out, the ship's average speed was determined.
The method of dead reckoning was recognized, then as now, as
yielding only approximate results.
As the New World was explored the latitudes of harbors, settle-
ments and promontories were reported to the king, and the approxi-
mate distances from Spain as well. So, if a voyage from Cadiz to
Vera Cruz was undertaken, the navigator would set out on a course
as much toward the southwest as he felt was right. Each noon of
the voyage he would make an observation on the sun for latitude.
This he would continue to do until the day came when his noon
observation told him that he was in the latitude of Vera Cruz.
He would then change his course and steer due west for that port.
If his first assumed course brought him to a landfall before enter-
ing the desired latitude, he sailed south along the coast until he
made his destination. An example of this mode of navigation is
El Cano's bringing Magellan's ships home through the Indian
Ocean. The chart of his voyage shows that he sailed southwesterly
until he found the latitude of the Cape of Good Hope, when he
changed his course to due west.
The early maps of Spanish explorations in America reflect the
difficulties of longitude determination by omitting the meridional
lines, yet latitude is nearly always indicated. The ancient notion
that the earth inclined toward the poles is contained in the word
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Texas State Historical Association. The Southwestern Historical Quarterly, Volume 29, July 1925 - April, 1926, periodical, 1926; Austin, Texas. (texashistory.unt.edu/ark:/67531/metapth117141/m1/95/: accessed October 16, 2018), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; crediting Texas State Historical Association.