Dr. Darwin’s ’Experiments , &c. 
effe<ft of the a&ivity of the retina may be to alter its thicknefs 
or thinnefs, fo as better to adapt it to refledl or tranfmit the 
colours which ftimulate it into aftion ? May not mufcular 
fibres exift in the retina for this purpofe, which may be lefs 
minute than the locomotive mufcles of microfcopic animals ? 
May not thefe mufcular actions of the retina conftitute the 
fenfation of lights and colours ; and the voluntary repetitions 
of them, when the object is withdrawn, conftitute our me- 
mory of them ? And laftly, may not the laws of the fenfa- 
tionsof light, here inveftigated, be applicable to all our other 
fenfes, and much contribute to elucidate many phenomena of 
animal bodies both in their healthy and difeafed ftate ; and thus 
render this inveftigation well worthy the attention of the phy- 
fician, the metaphyfician, and the natural philofopher ? 
Derby, November i 9 1785* 
