OF ARTS AND SCIENCES. 403 



sense of the Spiritualistic philosophy, we should, at the same time, 

 be compelled to admit that the eye is a somewhat clumsy organ. If 

 the ultimate fibres of the auditory nerve had been supposed to be di- 

 rectly sensitive only to the vibrations of the fluid of the labyrinth, and 

 if the functions of the ductus cochlearis and all its exquisite mechanism 

 — which does instantly what the mathematician only lately learned to 

 .work out by Fourier's intricate formulaj — had been undiscovered, the 

 explanation of the ultimate processes involved in the sensation of hear- 

 ing would be scarcely more satisfactory than those of the sensation of 

 color-perception now are. 



Purkinje, Volkmann, Helmholtz, and others have found that, if two 

 parallel fibres of spider's web, or two fine wires, be brought very close 

 together upon a white ground, the intermediate white line seems to 

 have a beaded, or zigzag, outline, when closely examined with one eye. 



Assuming the cones to be arranged somewhat in the form of hexag- 

 onal cells in a honey-comb, this has been exj^lained by supposing that 

 the retinal image of such a line is so small that, as it falls across this 

 rausive surface, one minute section of it would excite only one cone, 

 while the sections immediately above and below would cover halves of 

 two adjacent cones, and, exciting both to activity, would appear twice 

 as large. 



Now, if the ultimate percipient elements be cones of three varieties 

 of sensibility, corresponding to the colors red, green, and blue, or vio- 

 let, it follows that the cones which perceive, e. g. green, must be much 

 more widely dispersed over the retina, being at most only one-third of 

 the whole number ; and hence, with black lines upon green ground, or 

 the reverse, we might fairly expect this beaded irregularity to be much 

 greater than if all the cones were excited, as they would be by white 

 lines of light. To test this, I gummed ultimate fibres of white silk 

 upon a smooth piece of heavy black paper, as near together as I could 

 distinguish them when the lens under which I worked was removed. 

 By bending the paper gently backward, the fibres were drawn tense 

 and straight. After some practice, in the morning, when the eyes were 

 fresh, or even after closing them for a minute, later in the day, I could 

 distinctly recognize that the outlines of the white fibres were wavy, 

 and even beaded. Now, as near them as possible, parallel fibres of 

 bright red. green, blue, and violet were fastened, and viewed in a simi- 

 lar manner, under stronger illuminations. The same wavy outlines 

 were observed, though with somewhat greater straining of the eyes. 

 It is quite certain tliat the curves were no larger, and no less frequent, 

 than with the white fibres. Thus, if the cause assigned to these ap- 



