U CONCEPTIONS OF COLUMBUS 



of the length of a degree and that the erroneous in- 

 formation available in his day actually led him to 

 arrive at the old figure of 56^^ miles. 



At first sight, the opportunities open to Columbus 

 for determining the length of a degree may well have 

 seemed to promise accurate results. In the earlier 

 instances cited the observ^ed points were relatively 

 close — in the case of Eratosthenes, the interval was 

 about seven degrees; in the other, much less. Of 

 course, the shorter the distance, the greater became 

 the importance of any error. For the redetermi- 

 nation by Columbus, on the other hand, a much 

 greater interval was available — approximately forty 

 degrees, according to the obser^^ations of the Portu- 

 guese. In fact, with the exploration of the west 

 coast of Africa it became possible, for the first time 

 in history, to carry out obser\^ations and measure- 

 ments on a grand scale and o\'er an extended interv^al 

 practically free from obstructions. Hence, it is ob- 

 vious, great confidence might be placed in the results 

 obtained if, under the new conditions, the old value 

 should be arrived at. 



In the new determination the two fixed points 

 were Lisbon and the Los Idolos Islands (or Isles de 

 Los; ofT Konakry, French Guinea). The distance 

 must be presumed to have been measured by re- 

 peated dead reckonings, as this was the regular prac- 

 tice of the time. All that remained for Columbus to 

 do, in order to verify the length of a degree, was to 

 make a simple arithmetical calculation. In concrete 



