ther; or whether it is towed or sailing alone; or whether it
carries new or old sails and whether they are of good or ill pattern,
and wet or dry; whether the day's run is estimated from the poop,
prow, or amidships; and other special considerations that I pass by,
such as the heaviness or lightness of the winds, the differences in
compasses, etc. From the above then, I infer that it is difficult
and unsatisfactory to determine the size of the earth by means of
measuring it by traveling or sailing, and the same was maintained by
Ptolemaeus and other erudite men by actual test.

As to the second method, namely, by determining what portion of the
earth corresponds to another known part of the heavens, it is more
_probabile etiam per demonstrationem_. But the difficulty of this
method lies in the fact that this proof or demonstration has been
made by many learned and experienced men, and we discover a great
diversity in their results, as I pointed out in my opinion when it
was agreed that every one should commit _in scriptis_ the number of
leagues corresponding to each degree, of which the following is a copy.

[Here follow the different calculations of the length of a degree and
the circumference of the earth, beginning with Aristotle. Briefly
these are as follows: Aristotle, 800 stadia to a degree, making
the terrestial circumference, 12,500 leagues; Strabo, Ambrosius,
Theodosius, Macrobius, [189] and Eratosthenes, each 700 stadia to the
degree, and a circumference of 7,875 leagues; Marinus and Ptolemaeus,
500 stadia to the degree, and a circumference of 5,625 leagues;
Tebit, Almeon, Alfragano, Pedro de Aliaco [190] "in the tenth
chapter of _De imagine mundi_ and the author of the sphere in the
division of the zones," Fray Juan de Pecan "in the fourth chapter of
the treatise of the sphere," and the "first Admiral of the Indies,
[191] as is evident from many papers made by him," each "fifty-six
and two-thirds miles" or "fourteen leagues and two-thirds of a mile"
to a degree, and a circumference of 5,100 leagues. "If no opposition is
given to this latter _ex adverso mere voluntarie_," continues Colon,
"then necessarily we must have recourse to verify it by experience,
which is hindered by many obstacles." In further reasoning he says:]

It is clear from the above, that, supposing the measurement of the
degrees to be conclusive, it is not reduced to such practical form
that the place where such and such a number of league