787 



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 hu- 

 mour ; E F G is the choroid coat, lined by the retina; 

 li I K the sclerotica, and L the optic nerve. P, 447. 



Fig. 43r. A picture painted on the retina in an 

 inverted position, seen by dissecting off tlie sclerotica 

 and choroid behind it. P. 448. 



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. 454. 



Fig. 439. The red square A, inclosing a green square, 

 produces, if viewed attentively, in a strong light, a 

 spectrum resembUng B, which is red within and green 

 without, and which appears when we look soon after 

 cn any white object. P. 456. 



Fig. 440. Tlie spot, wliich is tinted with blact lines 

 only, appears, upon the yellow grouud, of a purple 

 hue. P. 456. 



Fig. 441. A grey spot on a purple ground appears 

 of a greenish yellow or olive hue. V. 456. 



Fig. 442. The manner in which two portions of 

 coloured liglit, admitted through two small apertures, 

 produce light and dark stripes or friivges by their in- 

 terference, proceeding in the form of hyperbolas; the 

 middle ones are however usually a little dilated, as at 

 A. P. 465. 



Fig. 443. A series of stripes of all colours, of their 

 appropriate breadths, placed side by side in the man- 

 ner in which they would be separated by refraction, 

 and combj^ncd together so as to form the fringes of 

 xolourB bcluw them, beginning from white. P. 465. 



Fig 444. A series «fcoronae, seen round the sun sr 

 moon. P 466. 



Fig. 445. The internal hyperbolic fringes of a rect- 

 angular shadow. P. 467. 



Fig. 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 magnitude of the shadow, independently of 

 diffraction. P. 468. 



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. 469. 



Fig. 448. The coloured stripes of a film of soapy 

 water, covering a wine glass. P. 469. 



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. 469. 



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 colouris the 

 contrast to that of the opposite half of the ring. P. 470. 



Fig. 451. The composition of the colours of the 

 primary rainbow, when attended by supernumerary 

 bows. P. 471. 



Fig. 452. The colours of concave mirrors. The 

 small circles in the middle white ring represent the 

 aperture by which the light is adrnitted, and its image ; 

 the coloured rings are formed by the light irregularly 

 dissipated, before and after reflection. P. 471. 



