, ocular Speffra of Light and Colours . 3.3.5 
'rtiefe circumftances, though they very much perplexed the 
experiments till they were inveftigated, admit of a fatisfadory 
explanation ; for while the rays from the bright internal ob- 
j ie£l in exp. fall with their full force on the center of the 
retina, and, by fatiguing that part of it, indue e the reverfe > 
fpedrum, 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 fpedrum of the pink colour in thofe parts of the 
eye. The fame reverfe and direct fpedra occur from the violet 
paper in exp. b< : and in exp. r. the fcattered rays from the 
central pink paper produce a dired fpedrum of this colour on 
the external parts of the eye, while the fcattered rays from 
the external blue paper produce a direct fpedrum of that colour 
on the central part of the eye, inftead of thefe parts of the 
retina falling reciprocally into their reverfe fpedra. In exp. d» 
the colours being the reverfe of each other, the fcattered rays 
from the exterior objed falling on the central parts of the eye, 
and there exciting. their dired fpedrum, at the fame time that 
the retina, was excited into a reverfe fpedrum by the central 
objed, and this dired and reverfe fpedrum being * of fimilar 
colour, the fuperior brilliancy of this fpedrum was produced. 
In exp. e . the effed of various quantities of ffimnlus on the 
retina, from the different refpedive. fizes of the internal and 
external areas, induced a fpedrum of the internal area in the 
center of the eye, combined of the reverfe fpedrum of that in- 
ternal area and the dired one of the external area, in various 
fhades of colour, from a pale green to a deep blue, with fimi- 
lar changes in the fpedrum of the external area. For the fame 
reafons, when an internal bright objed was final 1, as in exp ,f 
hifiead of the whole of the fpedrum of the external objed 
