CH. v. PTOLEMY AND STRABO. 33 



must remember that it had the same effect whether you 

 moved round the ball, or the ball round you in our experi- 







ment on page 1 9 ; and Ptolemy's explanations were apparently 

 so near the truth that astronomers were satisfied with them for 

 1,400 years, till Copernicus discovered the real movements. 



Ptolemy was a geographer as well as an astronomer ; 

 he wrote a book on geography which was used in all the 

 schools of learning for nearly fourteen hundred years. He 

 drew maps of all the known parts of the world, and laid 

 down on them lines of latitude and longitude, which he cal- 

 culated by the rules Eratosthenes had discovered. In his 

 geography he describes the countries from the Canary Islands 

 on the west to India and China on the east, and from Norway 

 to the south of Egypt. He describes our island under the 

 name of Albion, or Britain, and traces out many of the coast- 

 lines and rivers. He also gives the names of the various 

 towns, with their latitude and longitude. 



Strabo. A little before the time of Ptolemy there lived 

 a famous traveller named Strabo, who wrote a great deal on 

 geography. He was born at Amasia, in Cappadocia, and 

 was probably living when Christ was born. Strabo in his 

 book describes the countries which he visited and read about. 

 He also studied earthquakes and volcanoes, and pointed out 

 that, when the hot vapour and lava hidden in the crust of 

 our earth cannot escape, they cause earthquakes, but that 

 when they find their way out through a volcano, like Etna, 

 the country is not so often disturbed and shaken. 



Galen, 131. There is still one more great man of science 

 whom we must mention as belonging to the Greek school at 

 Alexandria. This was Galen, one of the most celebrated 

 physicians of antiquity. He was born A.D. 131, at Perga- 

 mos, in Asia Minor, and during his life he is said to have 



