GEOGRAPHICAL LATITUDE. 783 



Aristotle and Archimedes, for instance, thought the earth to be much 

 larger than the measurement of Eratosthenes showed it to be ; and 

 their abstract calculations, notwithstanding their general authority, 

 gave way in this matter before the better grounded result. Is it likely 

 that this latter would in turn be rejected without what was at least sup- 

 posed by the learned to be equally well-founded reasons ? 



Thus stood the matter at the close of classical times; and the litera- 

 ture of the subject was inherited by the Arabs, when they reached 

 their flourishing period, along with the great mass of Greek learning. 

 One of the early caliphs, Almanioun (813-833), who took an active inter- 

 est in scientific matters, ordered (A. d. 827) the measurenient of an arc of 

 meridian in order to determine independently the size of the earth. 

 Several different accounts of how this order was carried out have come 

 down to us and vary eonsid(?rably the one from the other. There 

 seem however to have been two sei)arate and distinct measurements 

 made, resulting respectively in 57 and 56;^ Arabic miU-s for the value of 

 a degree of latitude. ' As the mean, 56| miles was adoi)ted officially 

 for the length of a degree. But what was the true length of the Arabic 

 mile? It contained 4,000 so-called black cubits; a cubit, 4 palms ; a 

 palm, 4 j)olles; and a poUe, 6 barley grains laid side by side. But all 

 barley grains are not equal in thickness and as this variable quantity 

 is the foundation of the numerical system, modern experts have differed 

 greatly in the resulting value of a degree of latitude, the one giving it 

 at 54,503 toises, another at 63,750 toises, etc.'^ The method of procedure 

 was in each case as follows: Two parties were sent to the same start- 

 ing point and, having there observed the altitude of the sun (by what 

 means is not known), the one party measured^ toward the north, the 

 other toward the south, till by new observations they found they had 

 advanced 1 degree, where they ceased work and reported the distance 

 measured.* pjbu Jounis, who furnished the most detailed account of 

 the operation, describes also the precaution necessary to insure accu- 

 racy in the result, but leaves us in the dark as to w nether or not these 

 precautions were actually observed,^ Albategnius, who in most respects 

 was among the most accurate of the Arabic scientists, gives the length 

 of a degree at 85 miles, which however may be the result of a typo- 

 graphic error in the printed translation;^ while Edrisi is said to have 



'Delambre, 66, quotes '' Abilfedea" (Aboulfeda) as saying that the astronomers 

 found only 56 miles for the value of a degree. 



2 See Posch, 28 et seq. Delambre, Astrou. du moyeu-age, 66. 



^Peschel (133) and Delambre (78) give different accounts of the manner of meas- 

 uring the lino, the one by rules and stakes, the other by long cords, jilacing each 

 time the end of the last at the middle of the preceding to preserve a straight line. 

 Delambre gives another version, pp. 97,98. 



* Delambre, Astrou. du moyen-5,ge, 78; Bauernfeind, Die Bedeutiing moderner 

 Gradmessungen, p. 10; Posch, Geschichte uud System der Breiteugrad-Messungen, 

 28 ff; Peschel, Erdkunde, 133; Giinther, Studien, etc., 59,60. 



"Delambre, Astron. du moyen-4ge, 78. 



* Delambre, Astron. du xviii"'« sifecle, 15. 



