400 



THE SENSORIAL FUNCTIONS. 



line lens of the Cod, to which he was led by 

 noticing some remarkable optical appearances 

 presented by thin layers of this substance when 

 transmitting polarised light. He found that the 

 hard central portion is composed of a succession 

 of concentric, and perfectly transparent, sphe- 

 roidal laminae, the surfaces of which, though 

 apparently smooth, have the same kind of iri- 

 descence as mother-of-pearl, and arising from 

 the same cause ; namely, the occurrence of re- 

 gularly arranged lines, or strice* These lines, 

 which mark the edges of the separate fibres 

 composing each lamina, converge like meridians 

 from the equator to the two poles of the sphe- 



roid, as is shown in Fig. 431. The fibres them- 

 selves are not cylindrical, but flat; and they 

 taper at each end as they approach the points of 

 convergence. The breadth of the fibres in the 

 most external layer, at the equator, is about the 

 5,500th of an inch. The observation of another 

 optical phenomenon, of a still more delicate kind, 



* See vol. i. p. 232. 



