1896.] Principles of Geology audits Aim. 179 



Persia, and science was advanced by sending out expeditions 

 to explore and survey the various provinces he had conquered. 

 The Greeks he sent out, and also those who accompanied him, 

 were critical observers and carefully described the products 

 and aspects of the country, and made collections of all that 

 was interesting in regard to the organic and inorganic pro- 

 Ptolemy (323 B. C.) discovered Abyssinia and navigated the 

 Arabian Sea, and Silineus (306 B. C.) ascended the Ganges to 

 Batna and extended his expedition to the Indus. 



It was the military genius of the Romans which led to the 

 survey of nearly all Europe, and large tracts of Asia and 

 Africa. In the height of their power they had surveyed and 

 explored all the coast of the Mediterranean, Italy, the Balkan 

 peninsula, Spain, Gaul, West Germany and Britain, and their 

 practical genius led them to the study of the natural resources 

 of every province and state brought under their sway. 



Eratosthenes (276 B. C.) considered the world to be a sphere 

 revolving with its surrounding atmosphere on one and 

 the same axis and having one center. His theories were per- 

 fected by Hipparchas (160 B. C). He attempted to catalogue 

 the stars and to fix their relative position, and he applied to 

 the determining of every point on the surface the same rule he 

 introduced in the arrangement of the constellation. 



Strabo (60 B. C.) noticed the rise and fall of the tide, and 

 maintained that the land changed its level and not the sea, and 

 that such changes happened more easily to the land beneath 

 the sea on account of its humidity. 



Ptolemy (150 A. D.) was the first scientific geographer. He 

 followed the principles of Hipparchas, which had been ne- 

 glected during the two centuries and a half since his time, 

 even by Strabo and Pliny. In Ptolemy's work is found for 

 the first time the mathematical principle of the construction 

 of maps, as well as several projections of the earth's surface. 



After the great achievements of Ptolemy to the 13th cen- 

 tury, the cultivation of the physical sciences was neglected. 

 In the 10th century Avicenna, Almar, and other Arabian 

 writers commented on the works of the Romans, but added 

 little of their own. 



