ABSTRACT
So far is Cheselden from supposing, for a moment, that the color we are conscious of, when looking through a glass of broken jelly, is not extended; that, on the contrary, he expressly asserts, that the light is so differently refracted by ‘a great variety of surfaces,’ that the several distinct pencils of rays CANNOT BE COLLECTED. Thus, upon the evidence of Cheselden, it is because of the DIFFUSION OR EXTENSION of color in the mind that the shape of any object SEEN THROUGH a cataract cannot be discerned: for, to say that the rays of color ‘cannot be collected,’ is manifestly but another mode of saying that they are scattered or extended (Fearn 1820, II.1: 147). Moreover, this is the language used by Reid himself to describe the case of
the person affected by cataract: ‘the “Chrystaline [ . . . ] does not exclude the rays of light but DIFFUSES THEM OVER THE RETINA.” Now what is DIFFUSION, but EXTENSION? And what, but some overwhelming bias, could have betrayed Dr. Reid into so glaring contradiction, as that of denying the extension of color in face of this concession?’ (Fearn 1820, II.1: 147-148). The bias Fearn alludes to is the ‘dogma of the inextension of the mind.’ But a different bias might be at work in Fearn’s critique: he presupposes that the extension of the physical impressions made by the rays of light on the retina necessarily implies that the color sensations in the mind are extended.39
