or Sectois of llaidiiiijer. 325 



obscure sectors as made blue by contrast. In order to test this 

 explanation, we must mention that M. Zokalski, an oculist m 

 Paris, found four persons from whose eyes the crystalline lens 

 had been extracted, and who nevertheless saw the phfenomenon 

 of the coloured sectors. Hence it follows that, as the inner sur- 

 face of the cornea has very little refraction, from its being in 

 contact with the aqueous humour, the sectors of M. Haidinger 

 must be produced, on M. Jamin's hypothesis, almost solely by 

 the anterior surface of that membrane. 



Ingenious as this explanation is, it is liable to the following 

 objections : — 



1. The magnitude of the sectors does not vary, as it ought to 

 do, with the aperture of the pupil, and with the area of the po- 

 larized beam. 



2. The yellow sectors ought in every position of the eye and 

 of the polarizing prism to have the same form in all sound cor- 

 neas : but in the Abbe Moigno's eye, the obscure sectors stretch 

 across the centre and separate the yellow ones ; and in my obser- 

 vations the pha;nomenon varies, as already described, with the 

 motion of the head or of the polarizer. 



3. The yellow colour of the sectors is not that which is pro- 

 duced by the I'efraction of polarized light. Their colour is the 

 yellow of the second order of Newton's scale, whereas the yellow 

 produced by refraction, even at the inaximum polarizing angle, 

 has an entirely different hue. But even if the colours were the 

 same, a single refraction, or even several at such a small angle 

 of incidence as that at which the rays are refracted by the cornea, 

 could not produce a visible tint. 



4. The blue sectors being, according to Jamin, brilliant, and 

 certainly as bright as the yellow ones, it is impossible that their 

 colour can be produced by contrast. I have made many expe- 

 riments with yellow and obscure sectors of various relative inten- 

 sities, and I cannot perceive anj'thing resembling the blue sectors 

 m question. 



5. If the sectors arc produced by refraction, the angular mag- 

 nitude of the yellow ones ought to be greater than 65 degrees, 

 and ought even to exceed that of the obscure ones. This result 

 I have put to the test of direct experiment, by transmitting po- 

 larized hght through various combinations of very small and very 

 convex surfaces of glass. Even wlien these surfaces are numerous, 

 tiie luminous sectors are greatly larger than the obscure ones. 



0. If the yellow sectors are jiroduced by the refraction only 

 of the cornea, their feeble tint should be increased by placing 

 before the eye a number of concavo-convex surfaces like those of 

 the cornea. I have made this experiment, but no change is 

 produced either in the form or intensity of the sectors. 



