128 DISCOVERY 



are the outstanding contributions of Arabia to physical 

 science in a period during which the Arabs were in 

 advance of the whole world in intellectual and industrial 

 activity. It was chiefly upon the researches of Alhazen 

 that Roger Bacon based the principles of optics 

 expounded by him. This Franciscan Friar of the thir- 

 teenth century anticipated many later discoveries in 

 physics and chemistry, and though he did not actually 

 discover the telescope, he described in detail, in his Opus 

 Majtis (1276), the properties of lenses and how they could 

 be used to make objects appear nearer, as in the case of 

 a simple magnifying glass. 



Adelard of Bath, who translated Euclid's Elements of 

 Geometry from Arabic into Latin early in the twelfth 

 century four hundred years before the Greek text was 

 recovered ; Robert Grosseteste, the illustrious Bishop 

 of Lincoln and author of an encyclopaedic Compendium 

 Scienlifiritm ; Peter Peregrinus of Maricourt, of whom 

 Bacon said : " Through experiment he gains knowledge 

 of natural things, medical, chemical, indeed of everything 

 in the heavens or earth," all preceded Bacon in their 

 scientific observations and writings and influenced his 

 thought. He was not really a great experimenter, and 

 his positive additions to natural knowledge are few, but 

 he was one of the first philosophers to insist upon the 

 value of experiment in scientific investigation. ' We 

 have," he said, " three means of knowledge authority, 

 reasoning, experiment. Authority has no value unless 

 its reason be shown ; it does not teach : it only calls for 

 assent." Again " Armed with experiment and calcula- 

 tion, science must not be content with fac+s, though these 

 may have their utility ; it seeks truth ; it wants to find 

 out the laws, the causes canones, universales regulae." 



In the bold appeal which Roger Bacon made to experi- 



