ASTRONOMY, ETC. 
109 
word ’Aa-Tpovofiia (Suidas), which latter word is perhaps a mis 
take for ’Aa-TpoOecria corresponding to the title ’Aa-Tpodecricu 
{cpSicov found in the manuscripts. The work as we have it 
contains the story, mythological and descriptive, of the con 
stellations, &c., under forty-four heads; there is little or 
nothing belonging to astronomy proper. 
Eratosthenes is also famous as the first to attempt a scientific 
chronology beginning from the siege of Troy; this was the 
subject of his XpovoypafyiaL, with which must be connected 
the separate ’OXvpmovLKou in several books. Clement of 
Alexandria gives a short resumS of the main results of the 
former work, and both works were largely used by Apollo- 
dorus. Another lost work was on the Octaeteris (or eight- 
years’ period), which is twice mentioned, by Geminus and 
Achilles; from the latter we learn that v Eratosthenes re 
garded the work on the same subject attributed to Eudoxus 
as not genuine. His Geographica in three books is mainly 
known to us through Suidas’s criticism of it. It began with 
a history of geography down to his own time; Eratosthenes 
then proceeded to mathematical geography, the spherical form 
of the earth, the negligibility in comparison with this of the 
unevennesses caused by mountains and valleys, the changes of 
features due to floods, earthquakes and the like. It would 
appear from Theon of Smyrna’s allusions that Eratosthenes 
estimated the height of the highest mountain to be 10 stades 
or about 1 /8000th part of the diameter of the earth.