rr 
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£.. L. Nichols—Color Impressions upon the Retina. 245 
the slit of the spectroscope at the rate of two or three revolu- 
_ ihe portions of the spectrum chosen for comparison were 
situated as follows: 
Spectral region. caeuieat: : settvacae: 
Bed oii Sh a ae 420 
Orange? 2 Sant. 6463 
KOHOW iss Gers Uri ee ae 6025 
FOG: Guns cee ie 5415 
BiG) oie kale 4784 
WIE Soe ee ecco 4382 
hragm in the eye-piece of the spectroscope enabled 
A dia 
the heat vee to exclude, during the course of each experiment, 
all parts of the spectrum not under observation. 
_ _ It was found by experience that the lowest velocity produc- 
ing continuity of vision could be best determined by taking 
advantage of the following phenomenon. The transition from 
