I

OF THE EXTERNAL SENSES. 277

pi, the externality of their exjftence is immediately

*{ perceived by our Sight . But if we conlider that

r.:a the diftance of any object from the eye, is a line

h.j turned endways to it; and that this line muft con-

fequently appear to it, but as one point; we fhallbe fenfible that diftance from tire eye cannot bethe immediate objeft of Sight , but that all vifibleobjects muft naturally be perceived as clofe upon£5, the organ, or more properly, perhaps, like all other

Senfations, as in the organ which perceives them.hit That the objefls of Sight are all painted in the

lf: t bottom of the eye, upon a membrane called the

retina, pretty much in the fame manner as the» like obje&s are painted in a Camera Obfcura, is

et well known to whoever has the flighteft tincture

'!• of the fcience of Optics; and the principle of per-

td ception, it is probable, originally perceives them,

is as exifting in that part of the organ, and nowhere

na but in that part of the organ. No Optician, ac-

3 cordingly, no perfon who has ever bellowed any

- moderate degree of attention upon the nature of

o Vifion, has ever pretended that diftance from the

by eye was the immediate objedl of Sight . How it

is that, by means of our Sight , we learn to judgeis offuch diftances, Opticians have endeavoured to

it- explain in feveral different ways. I fhall not,

ot however, at prefent, flop to examine their fyl-

ii terns.

;• The obje£ls of Touch are folidity, and thofe

modifications of folidity which we confider as ef-fential to it, and infepaiable from it; folid ex-tenfion, figure, diviftbility, and mobility.