754 GEOGKAPHICAL LATITUDE. 



then iu vogue. Accepted as true, it was made the basis of the geo- 

 graphical latitude of antiquity. The parallel of Syene was hence con- 

 sidered the Tropic of Cancer, and from this point distances and degrees 

 were computed north and south. 



The only scientific method then known of determining latitude 

 was by observing the length of shadow cast, either at the equinox 

 or summer solstice, by a simple instrument called a gnomon. It 

 has been suggested that the obelisks of Egypt served this purpose.^ 

 Two varieties of this instrument are mentioned as in use among 

 the ancients. One was formed by a hollow hemisphere having in 

 its center an upright whose length was e(iual to the radius of the 

 sphere; so that the proportional length of the shadow to the distance 

 between the base of the upright and the periphery of the hemisphere, 

 as observed at the summer solstice, gave the proportion of the 

 distance of the place of observation between the Tropic of Cancer 

 and the north lyole. This instrument is said to have been imported 

 from the Chaldeans,'^ and used only by Eratosthenes among the Greeks.^ 

 The usual form of gnomon had a flat base, and the latitude of the 

 place of observation was indicated by the ratio of the length of 

 the shadow to the upright, as observed at the equinox. Whether 

 this instrument was brought from the East or invented inde- 

 pendently in Greece, it seems impossible to decide. There is prob- 

 ably no good reason for doubting that it was already in use 

 among the Chinese eleven hundred years before Christ.* But with 

 them directly the Greeks had no intercourse. Bailly, who finds the 

 beginning of all things in the Orient and allows the Greeks no in- 

 ventive genius whatever, relates that Pherecides erected such an in- 

 strument on an island in the Syrian Sea, and that Anaximander 

 perhaps carried the knowledge thereof to Greece,* while Pliny ascribes 

 its invention to Anaximenes of Miletus, a pupil of Anaximander,^ and 

 a modern investigator of great learning maintains that Pytheas"is 

 the first of whom it is historically certain that he determined the 

 altitude of the pole of a place by the length of the sun's shadow." "^ 



'Delambre, Astron. ancienne, i, 14. Cassini, Griaudenr, etc., 33. One brought 

 from Egypt by order of Augustus, was placed on what is now the Champ de Mars and 

 used for that purpose by Manilius. Wolf, Gesch. d. Astronomie, 124. 



2 Manner t, i. 11 J. 



^''C'est Ph^misphere creux de B^rose." Delainbre, Astron. ancienne, i, 221. 

 Ideler is of another opinion. "Sic (die Skaphe) war eine Erfindung des Jns<arcft 

 von Samos. Von ihrer Gestalt hiess sie auch Hemisphaerium ; denn sie bestand aus 

 einem sphiirischgekriimmten metalleuen Beckeu, auf dessen Boden in der Richtung 

 und Liinge des Halbmessers ein Stift, rvcb/noov, a\a Schatteuzeiger, errichtet war." 

 Zach, Mon. Cor., May, 1811, citing as authority Martiauus Capella, de Nupt., i, vi, p. 

 194. Ed Grotii. 



^Delambre, Astron. ancienne, i, xvii. Kirchhoff, Uuser Wissen von der Erde, 1. 15. 



6 Bailly, Histoire de I'astrou., 197, 198. 



"Strack's Pliuius, I. 115; lib. ii. 76-78. 



' Mannert, i. 5. 



