292 THOMAS YOUNG. 
ing ever, like the philosopher of Egina, proudly closed 
their school against all who 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 ts presents sufficient diffi- 
culties to render it at least somewhat presumptuous to 
east ourselves upon the world of intelligences to search 
after what ought to be ; 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, Maurolyeus 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 
