292 THOMAS YOUNG. 



ing ever, like the philosopher of Egina, proudly closed 

 their school against all wlio were not geometers, careful 

 experimenters marked out the sole route by which it is 

 permitted to man to arrive without false steps at the con- 

 quest of unknown regions of truth ; there Maurolycus 

 and Porta proclaimed to their contemporaries that the 

 problem of discovering what is presents sufficient diffi- 

 culties to render it at least somewhat presumptuous to 

 cast ourselves upon the world of intelligences to search 

 after what ought to he ; there these two celebrated fellow 

 countrymen of Archimedes commenced the explanation 

 of the functions of the different media of which the eye 

 is composed ; and showed themselves contented, as were 

 at a later period Galileo and Newton, not to ascend 

 above those kinds of knowledge which are capable of 

 being elaborated or corrected by the aid of our senses, 

 and which had been stigmatized under the porticos of 

 the Academy by the contemptuous epithet of simple 

 opinion. Such is always human weakness that, after 

 having followed with a rare success the principal devia- 

 tions which light undergoes in passing through the cornea 

 and the crystalline, Maurolycus and Porta, when very 

 near attaining their object, stopped short, as if before an 

 insurmountable difficulty, when it was objected to their 

 theory that objects ought to appear in an inverted posi- 

 tion if the images formed in the eye are themselves 

 inverted. The adventurous spirit of Kepler, on the 

 contrary, did not remain embarrassed. It was from 

 psychology that the attack originated ; it was equally 

 from psychology — clear, precise, and mathematical — that 

 he overthrew the objection. Under the powerful hand 

 of this great man, the eye became, definitively, the 

 simple optical apparatus known by the name of the 



