vvhich fliewM, lhadootmeafur'd itexadilyi but if it were but a 
quarterof a line or kfs, it fufficeth that it hadenoughfor theef- 
fedl I did attribiite to its Andforanother^I did alfo mention in 
my Writing, which is^ that the Rsyes of the fame luminous 
pointjWhich do not unite precifely in the fame points in the Axis^ 
areredlified by the concavity of the Retina^ thofe that are far- 
theft off the Axis more than thofe which are theneareft, which 
is the reafon t hey unite better in the fame point on the chorocs- 
dest, the which point I hold fwithyou ) to h^Hyfical, fince 
the points objedive aie fo too % but I hold it to be kffer than any 
that can be perceptible to the fight 5 for we diftinguifli the dif- 
ferent parts of very fmall objeifls, as the extremities of the 
breadthof the little arteries of the i?^^/;?^, which make not an 
eigth part of its thicknefs> and that which reprefents this 
fmall breadth, muft be 25 orj© times lefs in the Organ of pur 
fightjthat is to fay, in the proportion of the diftance of the 
Objeftp to the Centre of the fight^ and of the diftance of this 
Centre, to the Organ of vifion 5 artd by confequence the thick- 
nefs of the Retim is not proper for this fmallnefs. 
You fee, then Sir,that hitherto your obje£iicns have been able 
but ¥ery lightly to fhake my opinion, and that the tranfparency 
of the Retina-is well enough eftabliftied : Let us come now to the 
proofjl make of the Want of Yifton-;^ on the Bafis of the Optick 
Nerve. 
It muft firft of all be agreed, that in this Experiment, almoft? 
alloaen do loofe fight of an intire circle of white paper, whofe 
diameter is about the p^^or loth part of its diftance from the 
Eye, Now the vifual Triangle, whofe Bafis is the Diameter 
of the Circle, and whofe top is the Center of vifion^ is propor- 
tioned to the Triangle, whofe Bafis is the Diameter oi the pi- 
dure of the Circle on the bottom of the eye, and the top, the 
fame center of fight^ the wfcich center being diftant a or 7 lines 
from the bafis ot the optick nerve, whofe breadth is about ; of 
a line, this bafis alfo will be about the ^th or 10th part of its 
diftance from the Center of fight, and by the Principles of Op- 
ticks, the Im ^ge of the circle of the white paper, falling on the^ 
bafis of theopnck nerve, will cover it precifely-, and becaufe 
the Paper then wholly difappears; it follows, that all tbetefis 
I of 
