THE DETERMINATION OF THE LENGTH 



OF A TERRESTRIAL DEGREE 



BY COLUMBUS 



One of the essential questions which Christopher 

 Columbus was called upon to face in formulating his 

 project for a westward voyage was that of the distance 

 to be traversed between Europe and Asia. The cir- 

 cumference of the globe being taken as 360°, the prob- 

 lem resolved itself into (i) the calculation of the length 

 of a degree and (2) an estimate of the extension of 

 Asia eastward. The present study is a discussion of 

 the ideas of Columbus on these two points. 



Calculation of the Length of a Degree 



As is well known, Columbus took the length of a 

 degree to be 56^ Italian nautical miles. ^ This er- 

 roneous figure was not original with him; in fact, it 

 was a commonplace of medieval geography and goes 

 back to the ninth century of our era, when the as- 

 tronomers of the Caliph Al-Mamun determined this 

 value for the degree as a result of their historic sur\^ey 

 on the plains of Sinjar.- In the time of Colum- 

 bus the estimate of 56^ miles was commonly associ- 



1 See the section "The Statements of Columbus," pp. 6-11, below. 

 On the length of the Italian nautical mile see pp. 17-18, below. 



2 J. T. Reinaud and Stanislas Guyard, transls. : Geographie d'Aboul- 

 feda, traduite de I'arabe en frangais, 2 vols, in three, Paris, 1848-83; 

 reference in Vol. i (Introduction), pp. cclxix-cclxxiii. 



