A. M. Mayer—Researches in Acoustics. 251 
(which expresses our law), as we go from that ordinate belong- 
ing to the highest note to that belonging to the lowest, repre- 
sent the rate of successive extinctions of these harmonics in 
s on the color; lasting longer for red than for violet and 
onger for violet than for green. Here an analogy with our 
sonorous sensations is presented, for those stherial vibrations 
producing red are fewer in number than either green or violet, 
and the sensation of red lasts longer than either green or violet, 
and, therefore, it follows that we should have the residual 
image of the sun go through these changes—white, greenish- 
blue, blue, violet, purple, red; and this is what really happens 
when the sun’s image is momentarily formed on the retina and 
the eye then kept in darkness. nes : 
The above analogy is, however, imperfect if it really is estab- 
lished that the residual sensation of violet lasts longer than 
that of green, when the vibrations, giving these two colors, 
have equality of energy. The analogy also is one of sensations, 
not one of the mechanisms existing between the agents and the 
sensations they produce ; for, in the case of the ear, anatomical 
facts give us bases for the explanation of the ear’s power 0 
effecting a sonorous analysis, and for the understanding of the 
reason of our law of the duration of the residual sensation. 
prehend only ay and (2), but we know as yet nothing that gives 
us h ami 
structure of the human retina which point to the establish- 
ment of Young’s hypothesis of three distinct sets of retinal 
nerve terminations? The more we study the minute structure 
of the retinal rods and cones, the farther appears to remove an 
understanding of the mode of operation of the sensory apparatus 
of the eye. May not research in this direction be guided by the 
hypothesis that the molecular constitution of the retinal rods 
