780 GEOGRAPHICAL LATITUDE. 



on which level and changed to an arc the length of the line whose value 

 is sought is determined. 



There still remains the astronomical determination of the latitude of 

 the end points of the surveyed line, which is done by a great number 

 of observations, the mean is accepted as the final result. The differ- 

 ence in latitude compared with the length of the surveyed line, gives 

 the mean length of a degree of latitude in the meridian line surveyed. 



More than two thousand years have elapsed since the first scientific 

 attempt to measure the size of the earth. Interest in the matter has 

 increased with the spread of knowledge, while vast improvements in 

 science and art have gradually rendered possible the solving of the 

 l)roblem with great accuracy. The commencement of this grand work 

 was made by Eratosthenes (276-196 b. c), the librarian of the famous 

 library at Alexandria and a man whose talents found occupation in 

 several fields of science and art. Accepting the common belief that 

 Syene was on the Tropic, he observed at Alexandria with the hollow 

 gnomon at the summer solstice and found the shadow to be one fiftieth 

 of the circumference. The distance between the two places he valued 

 at 5,000 stadii, from which he deduced the earth's circumference, 

 250,000 stadii. How he arrived at the valuation of 5,000 stadii is 

 matter of dispute. General Baeyer, according to whose calculations 

 there was a failure in the given size of the earth's circumference of 

 only 8 geographical miles,' says he measured with rules, but fails to 

 give any authority for thestatement ; against which we have the author- 

 ity of Martianus Capella for the much more probable statement that he 

 learned the distance '^per mensores regios Ftolemcvi,''^^ and of Strabo, 

 who says he calculated it from the course of the Mle,^ while Kiepert 

 is of the opinion that he reached his result by comparing many inaccu- 

 rate lengths of the ways, gathered from various sources ; * to all which 

 may be added the assertion of Marcian of Heraclea, that he stole the 

 whole calculation from his predecessor, Timosthenes.^ However this 

 may be, the result remains the same, that in Eratosthenes's time there 

 was an attempt by scientific method to arrive at the size of the earth, 

 by which the circumference was determined to be 250,000 stadii, to 

 which he added 2,000 stadii, in order to have the convenient number 

 700 for the length of each degree.^ One is naturally curious to know 



^Behm's Geog. Jahrb., 1870., in, p. 155. 



«Zacb., Mou. Cor., 1811, p. 469. 



'Ideler, Zach, Mon. Cor., May, 1811, p. 469-70. "Nacli Strabo recbnete er auf den 

 Lanf des Nil von dem kleinen Kataracte in der Gegend von Syene bis an seinen 

 Ausflnss 5,300 Stadien. - - - Deun ZJawriHe versichert durch ein genanes Stndium 

 des iigyptiscben Terrains zwischen Syene und Alexandrieu uacb der Ricbtung der 

 Wego 640 roraiscbe Meilen oder 5,120 Stadien, und in gerader Richtung 560 romiecbe 

 Meilen oder 4,480 Stadien gefunden zu baben." 



^AlteGeog., .5. 



* Journal R. G. S., 1839, IX, p. 7, note. 



*Delanibre, Astron. ancienne, i, 221. Lelewel, G6og. dn nioyeu-itge, ix. Sprenger, 

 Ausland, 1867, p. 1067. Grosskurd's Strabo, i, 214, 215; lib. ii, Abt. iv, ^ 25. 



