THE BELFAST ADDRESS 163 



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

 All-Merciful will take pity on the soul of Abur-Kaihan, 

 because he was the first of the race of men to construct 

 a table of specific gravities." If all this be historic 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 Mohammedans." l 



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 re- 

 action 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 oppor- 

 tunity for the expression of opinion, the doctrine of "two- 

 fold truth" was invented, according to which an opinion 

 might be held u theologically, " and the opposite opinion 

 11 philosophically. "* Thus, in the thirteenth century, the 

 creation of the world in six days, and the unchangeable - 

 ness of the individual soul, which had been so distinctly 

 affirmed by St. Thomas Aquinas, were both denied phil- 

 osophically, but admitted to be true as articles of the 

 Catholic faith. When Protagoras uttered the maxim which 

 brought upon him so much vituperation, that " opposite 

 assertions are equally true," he simply meant to affirm 

 men's differences to be so great, that what was subject- 

 ively true to the one might be subjectively untrue to the 

 other. The great Sophist never meant to play fast and 

 loose with the truth by saying that one of two opposite 



1 "Intellectual Development of Europe," p. 359. 

 9 "Lange, 2d edit., pp. 181, 182. 



