Sect. XL. 10. i. OCULAR SPECTRA. 457 



b. When fix inches fquare of deep violet polifhed paper were 

 viewed on a foot fquare of white writing paper, the internal 

 fpectrum was yellow, being the reverfe fpectrum of the violet 

 paper, and the external one was violet, being the direct fpectrum 

 of the violet paper. 



c. When fix inches fquare of pink paper were viewed on a 

 foot fquare of blue paper, the internal fpectrum was blue, and 

 the external fpectrum was pink ; that is, the internal one was 

 the direct fpectrum of the external object, and the external one 

 was the direct fpectrum of the internal object, inftead of their 

 being each the reverfe fpectrum of the objects they belong- 

 ed to. 



d. When fix inches fquare of blue paper were viewed on a 

 foot fquare of yellow paper, the interior fpectrum became a bril- 

 liant yellow, and the exterior one a brilliant blue. The vivaci- 

 ty of the fpectra was owing to their being excited both by the 

 ftimulus of the interior and exterior objects ; fo that the interi- 

 or yellow fpectrum was both the reverfe fpectrum of the blue 

 paper, and the direct one of the yellow paper ; and the exteri- 

 or blue fpectrum was both the reverfe fpectrum of the yellow 

 paper, and the direct one of the blue paper. 



e. When the internal area was only a fquare half-inch of red 

 paper, laid on a fquare foot of dark violet paper, the infernal 

 fpectrum was green, with a reddiflr-blue halo. When the red 

 internal paper was two inches fquare, the internal fpectrum 

 was a deeper green, and the external one redder. When the 

 internal paper was fix inches fquare, the fpectrum of it became 

 blue, and the fpectrum of the external paper was red. 



J'. When a fquare half-inch of blue paper was laid on a fix- 

 inch fquare of yellow paper, the fpectrum of the central paper 

 in the clofed eye was yellow, incircled with a blue halo. On 

 looking long on the meridian fun, the difk fades into a pale blue 

 furrounded with a whitilh halo. 



Thefe circumftances, though they very much perplexed the 

 experiments till they were investigated, a"dmit of a fatisfactory 

 explanation ; for while the rays from the bright internal object 

 in exp. a. fall with their full force on the centre of the retina, 

 and, by fatiguing that part of it, induce the reverfe fpectrum, 

 many fcattered rays, from the fame internal pink paper, fall on 

 the more external parts of the retina, but not in fuch quantity 

 as to occafion much fatigue, and hence induce the direct fpec» 

 trum of the pink colour in thofe parts of the eye. The fame re- 

 verfe and direct fpectra occur from the violet paper in exp. b, : 

 and in exp. c. the fcattered rays from the central pink paper 

 produce a direct ipectruin of this colour on the external parts 



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