456 FRAGMENTS OF SCIENCE. 



Jove and the Most High God/ 7 Draper traces still further 

 than Whewell the Arab elements in onr scientific terms. 

 He gives examples of what Arabian men of science accom- 

 plished, 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 fifty-eight and 

 one-half miles. In the " Book of the Balance of Wisdom," 

 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 which plunged bodies rise 

 through heavier media. He understood the doctrine of 

 the center of gravity, 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 

 attraction. He improved the hydrometer. The determi- 

 nations of the densities of bocues, as given by Alhazen, 

 approach very closely to our own. " I join," says Draper, 

 " in the pious prayer of Alhazen, that in the day of 

 judgment the All-Merciful will take pity on the soul of 

 Abur-Raihan, because he was the first of the race of men to 

 construct a table of specific gravities." If all this be his- 

 toric truth (and I have entire confidence in Dr. Draper), 

 well may he "deplore the systematic manner in which the 

 literature of Europe has contrived to put out of sight our 

 scientific obligations to the Mahommedans." * 



The strain upon the mind during the stationary period 

 toward ultra- terrestrial things, to the neglect of problems 

 close at hand, was sure to provoke reaction. But the 

 reaction was gradual; for the ground was dangerous, and a 

 power was at. hand competent to crush the critic who went 

 too far. To elude this power, and still allow opportunity 



*" Intellectual Development of Europe," p. 359 



