4 
= 
a 
4 
3 
“4 
d 
W. LeConte Stevens— Physiological Optics. 349 
reversed and made as gradual as is desired by slowly increas- 
ing the convergence of visual lines and carrying it beyond the 
tem, ciliary contraction should modify also the impression 
ac 
mholtz has determined approximately the velocity of prop- 
agation of a nerve impression, but bevond this there has been 
little success in bringing the physiology of sensation within the 
domain of mathematical law. 
