THE BELFAST ADDRESS. 151 



physical image; in the other the image is distinct, the 

 descent and rise of the barometer being clearly figured 

 beforehand as the balancing of two varying and oppos- 

 ing pressures. 



3. 



During the drought of the Middle Ages in Christen- 

 dom, the Arabian intellect, as forcibly shown by 

 Draper, was active. With the intrusion of the Moors 

 into Spain, order, learning, and refinement took the 

 place of their opposites. When smitten with disease, 

 the Christian peasant resorted to a shrine, the Moorish 

 one to an instructed physician. The Arabs encour- 

 aged translations from the Greek philosophers, but 

 not from the Greek poets. They turned in disgust 

 ' from the lewdness of our classical mythology, and de- 

 nounced as an unpardonable blasphemy all connection 

 between the impure Olympian Jove and the Most High 

 God.' Draper traces still farther than Whewell the 

 Arab elements in our scientific terms. He gives ex- 

 amples 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 elevation, and actually fixed its height 

 at 58 miles. In the ' Book of the Balance of Wis- 

 dom,' he sets forth the connection between the weight 

 of the atmosphere and its increasing density. He 

 shows that a body will weigh differently in a rare and 

 dense atmosphere, and he considers the force with 



