xxxiv DESCRIPTION OF PLATES. 



PLATE XXX. 



Fig. 436. A section of the human eye. A is the cornea ; B the aqueous humour, 

 in which the uvea hangs ; C the crystalline lens ; the ciliary processes being between 

 it and the uvea ; D the vitreous humour ; E F G is the choroid coat, lined by the 

 retina ; H I K the sclerotica, and L the optic nerve. P. 350. 



Fig. 437. A picture painted on the retina in an inverted position, seen by dissect- 

 ing off the sclerotica and choroid behind it. P. 351. 



Fig. 438. The apparent figure of the heavens being nearly like the curve ABC, 

 the sun or moon at A or C appears to be much larger than at B. P. 356. 



Fig. 439. The red square A, inclosing a green square, produces, if viewed atten- 

 tively, in a strong light, a spectrum resembling B, which is red within and green 

 without, and which appears when we look soon after on any white object. P. 357. 



Fig. 440. The spot, which is tinted with black lines only, appears, upon the 

 yellow ground, of a purple hue. P. 357. 



Fig. 441. A grey spot on a purple ground appears of a greenish yellow or olive 

 hue. P. 357. 



Fig. 442. The manner in which two portions of coloured light, admitted through 

 two small apertures, produce light and dark stripes or fringes by their interference, 

 proceeding in the form of hyperbolas ; the middle ones are however usually a little 

 dilated, as at A. P. 365, 



Fig. 443. A series of stripes of all colours, of their appropriate breadths, placed 

 side by side in the manner in which they would be separated by refraction, and com- 

 bined together so as to form the fringes of colours below them, beginning from white. 

 P. 365. 



Fig. 444. A series of coronae, seen round the sun or moon. P. 366. 



Fig. 445. The internal hyperbolic fringes of a rectangular shadow. P. 367. 



1Fig. 446. The external fringes seen on each side of the shadow of a hair or wire, 

 which is also divided by its internal fringes. The dotted lines show the natural mag- 

 nitude of the shadow, independently of diffraction. P. 367. 



Fig. 447. Analysis of the colours of thin plates seen by reflection, beginning from 

 black. A line drawn across the curved fringes would show the portions into which 

 the light of any part is divided when viewed through a prism. P. 368. 



Fig. 448. The coloured stripes of a film of soapy water, covering a wine glass. 

 P. 368. 



Fig. 449. The colours of a thin plate of air or water contained between a convex 

 and a plane glass, as seen by reflection. P. 368. 



Fig. 450. The colours of a mixed plate ; as seen by partially greasing a lens a 

 little convex, and a flat glass, and holding them together between the eye and the 

 edge of a dark object. One half of the series begins from white, the other from 

 black, and each colour is the contrast to that of the opposite half of the ring. 

 P. 369. 



Fig. 451. The composition of the colours of the primary rainbow, when attended 

 by supernumerary bows. P. 369. 



Fig. 452. The colours of concave mirrors. The small circles in the middle white 

 ring represent the aperture by which the light is admitted, and its image ; the 

 coloured rings are formed by the light irregularly dissipated before and after reflec- 

 tion. P. 370. 



