162 FRAGMENTS OF SCIENCE 



physician. The Arabs encouraged translations from the 

 Greek philosophers, but not from the Greek poets. They 

 turned in disgust "from the lewdness of our classical 

 mythology, and denounced as an unpardonable blasphemy 

 all connection between the impure Olympian Jove and the 

 Most High God." Draper traces still further than Whew- 

 ell the Arab elements in our scientific terms. He gives 

 examples of what Arabian men of science accomplished, 

 dwelling particularly on Alhazen, who was the first to 

 correct the Platonic notion that rays of light are emitted 

 by the eye. Alhazen discovered atmospheric refraction, 

 and showed that we see the sun and the moon after they 

 have set. He explained the enlargement of the sun and 

 moon, and the shortening of the vertical diameters of both 

 these bodies when near the horizon. He was aware that 

 the atmosphere decreases in density with increase of eleva- 

 tion, and actually fixed its height at 583^ miles. In the 

 *'Book of the Balance of Wisdom," he sets forth the con- 

 nection between the weight of the atmosphere and its in- 

 creasing density. He shows that a body will weigh differ- 

 ently in a rare and dense atmosphere, and he considers 

 the force with which plunged bodies rise through heavier 

 media. He understood the doctrine of the centre of grav- 

 ity, and applied it to the investigation of balances and 

 steelyards. He recognized gravity as a force, though he 

 fell into the error of assuming it to diminish simply as 

 the distance, and of making it purely terrestrial. He 

 knew the relation between the velocities, spaces, and times 

 of falling bodies, and had distinct ideas of capillary attrac- 

 tion. He improved the hydrometer. The determinations 

 of the densities of bodies, as given by Alhazen, approach 

 very closely to our own. *'I join," says Draper, "in the 



