xiv.] ON DESCARTES' "DISCOURSE." 325 



Thus, thought is existence. More than that, so far ae 



we are concerned, existence is thought, all our concep- 

 tions of existence being some kind or other of thought. 

 Do not for a moment suppose that these are mere 

 paradoxes or subtleties. A little reflection upon the 

 commonest facts proves them to be irrefragable truths. 

 For example, I take up a marble, and I find it to be 

 a red, round, hard, single body. We call the redness, 

 the roundness, the hardness, and the singleness, "quali- 

 ties " of the marble ; and it sounds, at first, the height of 

 absurdity to say that all these qualities are modes of our 

 own consciousness, which cannot even be conceived to 

 exist in the marble. But consider the redness, to begin 

 with. How does the sensation of redness arise? The 

 waves of a certain very attenuated matter, the particles 

 of which are vibrating with vast rapidity, but with very 

 different velocities, strike upon the marble, and those 

 which vibrate with one particular velocity are thrown off 

 from its surface in all directions. The optical apparatus 

 of the eye gathers some of these together, and gives them 

 such a course that they impinge upon the surface of the 

 retina, which is a singularly delicate apparatus, connected 

 with the termination of the fibres of the optic nerve. 

 The impulses of the attenuated matter, or ether, affect 

 this apparatus and the fibres of the optic nerve in a 

 certain way ; and the change in the fibres of the optic 

 nerve produces yet other changes in the brain ; and 

 these, in some fashion unknown to us, give rise to the 

 feeling, or consciousness, of redness. If the marble 

 could remain unchanged, and either the rate of vibration 

 of the ether, or the nature of the retina, could be altered, 

 the marble would seem not red, but some other colour. 

 There are many people who are what are called colour- 

 blind, being unable to distinguish one colour from 

 another. Such an one miolit declare our marble to be 



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