(1041) 
deny but they are very fmall, and that it is very hard to difcero 
the little holes through which they pafs,when the nerve is cue 
off above its infertion into the Eye 5 and bccaufe they often 
come o^t of thebafis by two feveral little holes, the diameter 
of each of which does not take up the fpace of above the eighth 
part of thediameter of the bafis 5 it follows, that if the reft of 
(he nerve were fenfible o^light, we fhould not loofe fight of a pa- 
per of two inches diameter at moft, at ten fo'ot diitance: and 
fometimes in fixing one eye on a little piece of Paper, two other, 
very little ones, feparated one from the other, would d.fappearj 
which is contrary to experience: for the default of vifion is con- 
tinued. Semg than the reafons which you alledg of this default 
of fight are either infufficient, or want an afliired foundation, it 
follows, that that which I propofemuftftand, at leaft,in refped 
of any thing you urge againft it. And to confirme it yet more, I 
will adde here fome reafons and obfervations,which are neither in 
tny letter nor in tryy writing. 
The firft obftrvation which is very common, is that of the 
Pupilla dilates it felf in the (hade, and contra(5ts it felf in a great 
light, and it is very hard to find the caufe of this unvoluntar jr 
motion, but bythe Hypothefis, that the choroeides is fenfible 
of light, for then it is eafy to conceive that it being hurt by too 
ftrODg a vifion, it may dilate or contrad: its fibers, which have 
one continuity with thofe of the forepatt of the uvca^ fo that it 
can contrail its aperture, and when it is not hui t, relax it again : 
whereas if the Retina be fuppofed to be the Organ of fight, it 
will be very difficult to explain how this contraftion is made. 
The fecond is that of the glafs bottle full of water, when a 
lighted candle is placed near its focus: for it is eafy to prove 
that if one hold his hand between the Candle and the bottle, he 
will feel more heat than it he held it in the re^ iprocal Focus 5 
that is to fay, the place where the Rayes,which have puffed 
thorough the bottle, make a great image of the fl.aneof the 
Candle appear inverted upon a whitefurfaceoppofed to i : tor 
I draw this confequence, that the Image of a Candle, which '^s 
painted on xh^Cheroeides of a dog,as 1 have prov'd to you,ma es 
a much greater imrrefTion on the Ret na of the dog, than on 
: that of him that lookcs on it and fees it very bright ; whence 1 
I " " 
