2 20 Thomas Henry Huxley 



it seems sufficiently plain that there are two entities, 

 bod)' and soul in man, matter and mind in the whole 

 universe ; and various types of intelligent dogmatists, 

 ranging from the sturdy if somewhat stupid shrewd- 

 ness of Dr. Johnson to the agile casuistry of Catholic 

 metaphysicians, have supported this simple verdict of 

 " common sense. " Trouble begins, however, with 

 any attempt to analyse the relations between what we 

 call " matter " and what we call " mind." It appears, 

 for instance, that what we call matter we only know 

 in terms of mind. In an essay on Descartes' s Discourse 

 oil Method, Huxley explains this by simple examples. 



" I take up a marble and I find it to be a red, round, hard, 

 siugle body. We call the redness, the roundness, the hardness 

 and the singleness, 'qualities' 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 con- 

 ceived to exist in the marble. But consider the redness, to be- 

 gin 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 par- 

 ticular velocity are thrown off from its surface in all directions. 

 The optical apparatus of the ej'e gathers some of these together, 

 and gives them such a course that they impinge upon the sur- 

 face of the retina, which is a singularly delicate apparatus con- 

 nected with the terminations 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 un- 

 known to us, give rise to the feeling, or consciousness, of red- 

 ness. If the marble could remain unchanged, and either the 

 vibrations 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 



