SECT. XL. io. OCULAR SPECTRA. 627 



tral part oftheeye,inftead of thefe parts of the retina 

 falling reciprocally into their reverfe fpectra. In exp. 

 */.the colours being the reverfe of each other, the fcat- 

 tered rays from the exterior object falling on the cen- 

 tral parts of the eye, and there exciting their direct 

 fpectrum, at the fame time that the retina was ex- 

 cited into a reverfe fpectrum by the central object, 

 and this direct and reverfe fpedrum being of fimi- 

 lar colour, the fuperior brilliancy of this fpectrum 

 was produced. In exp. e. the effect of various quan- 

 tities of ftimulus on the retina, from the different 

 refpedtive fizes of the internal and external areas, 

 induced a fpedrum of the internal area in the center 

 of the eye, combined of the reverfe fpectrum of 

 that internal area and the direct one of the external 

 area, in various fhades of colour, from a pale green 

 to a deep blue, with fimilar changes in the fpec- 

 trum of the external area. For the fame reafons, 

 when an internal bright object was frnall, as in exp. 

 f. inftead of the w r hole of the fpectrum of the ex- 

 ternal object being reverfe to the colour of the in- 

 ternal object, only a kind of halo, or radiation of 

 colour, fimilar to that of the internal object, was 

 fpread a little way on the external fpectrum. For 

 this internal blue area being fo fmall, the fcattercd 

 rays from it extended but a little way on the image 

 of the external area of yellow paper, and could 

 therefore produce only a blue halo round the yel- 

 low fpectrum in the center. 



If any one mould fufpedl that the fcattercd rays 

 from the exterior coloured object do not intermix 

 with the rays from the interior coloured object, and 

 thus affect the central part of the eye, let him look 

 through an opake tube, about two feet in length, 

 and an inch in diameter, at a coloured wall of a 

 room with one eye, and with the other eye naked ; 

 and he will find, that by fhutting out the lateral 

 light, the area of the wall feen through a tube ap- 

 pears as if illuminated by the funfhine, compared 



with 



