0. N. Rood—Amount of Time necessary for Vision. 159 
Case of A. G. F. Time in seconds. 
Response to appearance of a white card, ia gO 
voles = electric spark, . -- 203 
bee & ROUNd. ka cows ee ee 138 
“ “ touch upon the forehead,. - -- Pag 
tee ie ee 17 
anid sce eer ee 
when required to decide between white and red,.. °443 
nape aia Seas circle and triangle, -494 
: Se “ tones C and E,..- 3 
* 5 a oe ve “ CandCabove, *428 
pe penmente of a similar nature to those which I have here 
recorded have been made by several European experimentalists, 
but none, I believe, in exactly the same manner; and as 
subject seems worthy of attention I hope to pursue it further. 
Columbus, Ohio, May, 1871. 
Arr. XXIIL.—On the amount of Time necessary for Vision ; by 
Ocpen N. Roop, Prof. of Physics in Columbia College. 
’ssume, in optical and physiological experiments, that the dis- 
charge of a Leyden jar is an instantaneous act; but at the same 
ume, by the determination of the greatest suitable resistance, it 
"ul be possible to limit the discharge to its least possible dura- 
fon."* Th d 
= Subjective optical phenomena: for example, for the 
_ Meognition of Loewe’s rings (using cobalt glass); also the _— 
lhe Stucture of the crystalline lens can be detected when the 
: tis suitably presented to the eye. 
* Pogg. Annalen, Band exiii, p. 453. 
