C^^4^ ) 
of theOptick nerve Is infenfible of light; whence Iconcludej 
that the choroeides is the Principal Organ of fight > and that the 
Rctim '\'s^ nox^ feeing it is placed in that part, and is there appa- 
rently difpofed in like manner as to the reft of the bottom of 
the Eye. 
Toelude the force of this Argument, you alledge other cau- 
fes of this fault of fight 5 the two firft are almoft like one an- 
other. But it feems to me, that you fuppofe them without any 
ground : for, as I faid before,there are no fuch filaments of nerves 
to be feencomingoutof thebafis of the optick nerve- befides, 
they are not proper for vifion , fince they would leave in the 
parts of the Retina too great intervals empty • and its ncceffary, 
that every point oft he Objedi find afenfible point in the Organ 
of fight to unite his rayes there which is found in the ChoroeideSy 
which is anEspanfion of the fenfible part of the nerve into a 
continued membrane. Befides, the caufes of the defed of vifion 
cannot be found in thefe Hypothefes for in the firft, what rea- 
foncan be given, that there ftiould be no extremities ofnetves 
oppofite to the optick nerve, fince there would need only a fim» 
pie diredi continuation of fome of its fibers unto the Anteriour 
part of the Retina 5 and for the (econd (which is the particular 
©pinionj I fee not, how the voidfpace in the middle of the in- 
verted Tuft, can comprehend all that extent of the bafis whence 
itproceedsj and why the filaments begin not to receive the im- 
preflion of the luminous Rayes^ but upon the Extremity of this 
bafis, fince the rayes of a luminous point, which anit^ themfclves 
in a point at the bottom of the Eye^ come from divers points of 
the C hryftalline, and fo^ if one part of thefe rayes were oblique, 
the other ftiould be perpendicular, and if all the Rayes fliould 
fall perpendicular on the Organ of fight, there would be no vifi- 
on, fince there is never but one fingle Ray of thofe which unite in 
a po'nt, that falls perpendicular. But I fliallnot ialarge my felt 
to demonftrate thefe impoflibilitics, fince I am perfwaded, that 
ihefe inverted tuft6, and thefe filaments of which they are comr 
pofed, are but things without a foundationjand which you would 
have much a doe to fliew us. ^ 
The other Caufe which you bring, is the trunk of theveflels 
which proceed from the bafis> o£ the nerve. Yet you cannot 
