Extract from 'Of Colours'

58 I tooke a bodkin gh & put it betwixt my eye & the bone as neare to the Backside of my eye as I could: & pressing my eye with the end of it (soe as to make the curvature a, bcdef in my eye) there appeared severall white darke & coloured circles r, s, t, &c. Which circles were plainest when I continued to rub my eye with the point of the bodkin, but if I held my eye & the bodkin still, though I continued to presse my eye with it yet the circles would grow faint & often disappeare untill I renewed them by moving my eye or the bodkin.

59 If the experiment were done in a light roome so that though my eyes were shut some light would get through their lidds There appeared a greate broade blewish darke circle outmost (as ts), & within that another light spot srs whose colour was much like that in the rest of the eye as at k. Within which spot appeared still another blew spot r, <16> especially if I pressed my eye hard & with a small pointed bodkin. & outmost at vt appeared a verge of light

60 But on the contrary if I tryed the experiment in very darke roome the circle ts apeared of a Reddish light sr of a darkish blew & the middle spot r appeared lighter againe; & there seemed to be a circle of darke blew tv without the circle ts the outmost of all [I conceive (in the 60^th experiment) where the curvature of the Retina at ma & fn began & was but little the blew colour tv was caused; at ab & ef where the Retina was most concave, the bright circle ts was caused: at bc. & de where the Retina was not much incurved nor strained the darke blew circle sr was caused & at cd where the Retina was stretched & made convex the light spot r was caused. In the 59^th Experiment the spirits were perhaps strained out of the Retina at ab, ef, & cd or otherways made incapable of being acted upon by light & soe made a lesse appearance of light than the rest of the Retina]