a Difficulty in the theory of Vifion. 203 
light fiiall be admitted as juft and convincing, we (hall have 
frefti reafon to admire the wifdorn of the Creator in fo adapt- 
ing the aperture of the pupil and the different refrangibility of 
light to each other, as to render the pi&ure of objects upon 
the retina relatively, though not abfolutely, perfect, and fitted 
for every ufeful purpofe; 4t where, ” to borrow the words of 
our religious and oratorical philofopher Derham, “ all the 
glories of the heavens and earth are brought and exquifitely 
pictured.” 
Nor does it appear, that any material advantage would have 
been obtained, if the image of objects on the retina had been, 
made abfolutely perfect, unlefs the acutenefs of the optic nerve 
ftiould have been increafed at the fame time ; as the minimum 
vifibile depends no lefs on that circumftance than the other*. 
But that the fenfibility of the optic nerve could not have been 
much increafed beyond what it is, without great inconvenience 
to us, may be eafily conceived, if we only confider the forcible 
imprefiion made on our eyes by a bright (ky, or even the day 
obje&s illuminated by a ftrong fun. Hence we may conclude, 
that fuch an alteration would have rendered our fight painful 
inftead of pleafant, and noxious inftead of ufeful. We might 
indeed have been enabled to fee more in the ftarry heavens with 
the naked eye, but it muft have been at the expence of our 
daily labours and occupations, the immediate and necefiary 
employment of man. 
I fhall only mention farther, and obviate an objection to the 
diffufion of the rays upon the retina by the different refrangi- 
bility of light. It may be faid, that the ocular aberration, 
being a feparate caufe from any effect of the telefcope, fliould 
fubfift equally when we obferve a ftar through a telefcope as 
when we look at it with the naked eye ; and that therefore the 
Q q z fixed 
