rs to have studied most assiduously, it is, at any
rate, possible that he may have overlooked, in his own writings, the
expression of an opinion which has escaped his penetration in theirs. To
convince himself, then, how much he is mistaken in supposing that the
visual intuition of longitudinal and lateral extension is admitted by
all philosophers, he has but to turn to the works of Dr Brown and the
elder Mill. In arguing that we have no immediate perception of visible
figure, Dr Brown not only virtually, but expressly, asserts that the
sight has no perception of extension in any of its dimensions. Not to
multiply quotations, the following will, no doubt, be received as
sufficient:--"They (i.e. philosophers) have--_I think without sufficient
reason_--universally supposed that the superficial extension of _length
and breadth_ becomes known to us by sight originally."[28] Dr Brown then
proceeds to argue, with what success we are not at present considering,
that our knowledge of extension and figure is derived from another
source than the sense of sight.

[28] Brown's Lectures, Lecture xxviii.

Mr James Mill, an author whom Mr Bailey frequently quotes with
approbation, and in confirmation of his own views, is equally explicit.
He maintains, in the plainest terms, that the eye has no intuition of
space, or of the reciprocal outness of visible objects. "Philosophy,"
says he, "has ascertained that we derive nothing from the eye whatever
but sensations of colour--that the idea of extension [he means in its
three dimensions] is derived from sensations not in the eye, but in the
muscular part of our frame."[29] Thus, contrary to what Mr Bailey
affirms, these two philosophers limit the office of vision to the
perception of mere colour or difference of colour, denying to the eye
the original perception of extension in any dimension whatever. In their
estimation, the intuition of space is no more involved in our perception
of different colours than it is involved in our perception of different
smells or different sounds. Dr Brown's doctrine, in which Mr Mill seems
to concur, is, that the perception of superficial extension no more
results from a certain expanse of the optic nerve being affected by a
variety of colours than it results from a certain expanse of the
olfactory nerve being affected by a variety of odours.[30] So much for
Mr Bailey's assertion, that _all_ philosophers admit the perception of
extension in two dimensi