Extract from 'Quæstiones quædam Philosophiæ' ('Certain Philosophical Questions')

9 If I presse my eye on the left side (when I looke towards my right hand) as at a, then I see a circle of red as at c but within the red is blew for the capillamenta are more pressed at n & o & round about the finger then at a towards the midst of the finger. that parte of the apparition at q is more languid because the capillamenta at o are duller & if the finger move towards e two much it vanisheth at q & appeareth semicircular but if I put my finger at e or {b} the apparition wholly vanisheth. By puting a brasse plate betwixt my eye & the bone nigher to the midst of the {tunica} than I could put my finger I mad a very vivid impression <124r> But of an ellipticall figue because the edge of the plate with which I prest my eye was long & not round like my finger If I was in the darke & the impression be very strong towards the outside appeared a broade circle of purple next blew then greene then yellow, red like flame, yellow, greene, blew, purple which growing from a very darke by degrees to a lighte blew ends in a greene in the midst. The colours I suppose next the flameing red looke something the darker by reason of its splendor. And if the experiment bee done in the light so that though my eyes were shut yet some rays got through my eye lids the outmost purple would appeare of a colour inclining to blacknes by reason I suppose of the bordering light. also if the pressure was not very strong the greene & purple at a would not be preceived in the darke but it would be something lighter in the light than in other places of the eye as at v or w, & all the other outmost colours without strong pression bee but blew. but if the presion be strong in the light the apparition will but little vary from what it is in the darke. beyond all the colours as betweene o & e the light is stronger than in other places as at v or w, because the pressure helpes the motion from without but is not strong enough to turne it to colour