Atlantis — Birth and Death of Science : 99 



Pythias' own books, one of them entitled The Ocean, have been 

 lost, but he is quoted in the works of many other classical scholars. 

 What he had to say seems at first to have been accepted and believed, 

 but later, though he was often quoted, he was usually discredited be- 

 cause what he reported did not agree with accepted theory. Pythias' 

 work was reinforced by the work of another Greek geographer, Era- 

 tosthenes, who lived from 239 to 196 b.c. Eratosthenes left a descrip- 

 tion of the known world from the shores of the Atlantic to India in 

 a gazetteer in which he attempted to assign the latitude and longi- 

 tude of places throughout this expanse. Naturally his latitudes were 

 fairly good, whereas his longitudes were erratic because he lacked an 

 accurate mechanical method of keeping time. Eratosthenes not only 

 believed in a round world but also gave us the first accurate measure- 

 ment of its circumference. 



He did this in the following way. He knew that at the summer 

 solstice the sun stood directly overhead at a place on the Nile called 

 Syene. Syene was the ancient name for the city in Egypt now known 

 as Aswan. At this time and place the sun shining down on a vertical 

 well cast no shadow at all. Erecting a vertical pointer at Alexandria, 

 where he was working, he took an observation of the earth's shadow 

 at the time of the summer solstice and calculated that the distance 

 from Alexandria to Syene represented the 150th part of a great circle. 

 The average of repeated measurements between Alexandria and 

 Syene gave a value of 5,000 stadia. He therefore calculated that the 

 circumference of the earth was 250,000 stadia, which converts into 

 25,000 miles. 



Admittedly there exists some doubt about the definition and use 

 of the term stadia and consequently about its conversion into our 

 miles. It is possible that both the measures of Pythias and of Eratos- 

 thenes may have been less accurate than would appear from these 

 rough calculations. The point is that both of these ancient scholars 

 had a clear idea of the character of the world in which they lived and 

 used correct theoretical methods in their calculations. They represent 

 a high-water mark in classical geographic knowledge. 



Unfortunately for the progress of science Posidonius, who lived 

 about one hundred years before Christ, also believed in a round 

 world and made a calculation of it as being only 18,000 miles in cir- 

 cumference. Posidonius somewhat atoned for his error in the calcu- 

 lation of the earth's circumference by recording the first deep-water 

 sounding. He reported that the Sardinian Sea was 1,000 fathoms in 

 depth. 



