SECT. XL. io. OCULAR SPECTRA, ft 5 



for the afliftance of others, who may xvifh to repeat 

 them. 



I, Of dire ft and mverfe fpeflra exlflwg at the Jaws 

 time ; of reciprocal dlrstl fpedra ; of a combination 

 of direft and inverfe fpeftra ; of a fpeflral halo ; 

 rules to predetermine the colours of fpeftra. 



a. When an area, about fix inches fquare, of 

 bright pink Indian paper, had been viewed on aa 

 area, about a foot fquare, of white writing paper, 

 the internal fpectrum in the clofed eye was green, 

 being the reverfe fpectrum of the pink paper; and 

 the external fpeetrum was pink, being the direct 

 fpectrum of the pink paper. The fame circum- 

 ftance happened when the internal area was white, 

 and external one pink ; that is, the internal fpectrum 

 was pink, and the external one green. All the 

 fame appearances occurred when the { ink paper 

 was laid on a black hat. 



b. When fix inches fquare of deep violet polifhed 

 paper was viewed oh a foot fquare of white writing 

 paper, the internal fpectrum was yellow, being the 

 reverfe fpectrum of the violet paper, and the exter- 

 nal one was violet, being the direct fpectrum of the 

 violet paper. 



c. When fix inches fquare of pink paper was 

 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 fpec- 

 trum of the external object, and the external one was 

 the direct fpedtrum of the internal object, inflead of 

 their being each the reverfe fpectrum of the objects 

 they belonged to. 



d. When fix inches fquare of blue paper were 

 viewed on a foot fquare of yellow paper, the inte- 

 rior fpectrum became a brilliant yellow, and the 

 exterior one a brilliant blue. The vivacity of the 



fpectra 



