622 OCULAR SPECTRA. Seer. XL. 



VII. Tfe r//>fl tf//*r having been excited into aflion by 

 a Jlimulus fomewhat greater than the lajl mentioned 

 falls into various fuccejfive fpafmodic aflions. 



1. ON looking at the meridian fun as long as the 

 eyes can well bear its brightnefs, the difk firft be- 

 comes pale, with a luminous crefcent, which feems 

 to librate from one edge of it to the other, owing 

 to the unfteadinefs of the eye ; then the whole 

 phafis of the fun becomes blue, furrounded with a 

 white halo ; and on doling the eyes, and covering 

 them with the hands, a yellow fpectrum is feen, 

 which in a little time changes into a blue one. 



M. de la Hire obferved, after looking at the bright 

 fun, that the impreflion in his eye firft affumed a 

 yellow appearance, and then green, and then blue ; 

 and wifhes to afcribe thefe appearances to fome 

 affection of the nerves. (Porterfield on the eye, Vol. 



I* P-343-) 



2. After looking fteadily on about an inch fquare 



of pink filk, placed on white paper, in a bright 

 funfhine, at the diftance of a foot from my eyes, and 

 clofing and covering my eyelids, the fpcdtrum of 

 the lilk was at firft a dark green, and the fpectrum 

 of the white paper became of a pink. The fpec- 

 tra then both difappeared ; and then the internal 

 fpectrum was blue ; and then, after a fecond difap- 

 pearance, became . yellow, and laftly pink, whilft 

 the fpectrum of the field varied into red and green. 



Thefe fucceflions of different coloured fpectra 

 were not exactly the fame in the different experi- 

 ments, though obferved, as near as could be, with 

 the fame quantity of light, and other fimilar cir- 

 cumftanccs ; owing, I fuppofe, to trying too many 

 experiments at a time ; fo that the eye was not quite 

 free from the fpectra of the colours which were pre- 

 vioufly attended to. 



The 



