236 Form and Color in Nature. 



What you are, root and all, and all in all, 

 I should know what God and man is." 



But to my work. 



First, as to the concrete meaning of our other terms. By 

 form we mean usually that which occupies space with two 

 dimensions length and breadth ; or with three dimensions 

 length, breadth, and thickness. Your mathematical professor 

 will talk to you learnedly about the fourth dimension of 

 space, but we, who find it difficult enough at times to fill out 

 our three dimensions, will not envy him his fourth. 



I shall use the term to mean that which has length, breadth, 

 and thickness which has perceptible limitations in all direc- 

 tions. 



Anticipating somewhat for the sake of completeness, I will 

 add that we can perceive form in two ways : through vision 

 and through tactual perception or touch. 



By color we mean a modification of that which we call light, 

 the character of which I should experience difficulty in de- 

 fining, and of the definition of which I am happily relieved 

 at the moment, as I hope, by your knowledge. 



So far as I am aware, we perceive this modification of light 

 solely through vision. Going one step farther back, we ap- 

 prehend light, and color as a resultant of light, as produced 

 by waves or pulses of exceeding minuteness and great rapid- 

 ity, in a hypothetical medium called the ether, which is sup- 

 posed to pervade all space, and therefore to penetrate at least 

 between the particles of so-called solid bodies, if it does not 

 pass through these particles. For I must call your attention 

 to the fact that the deeper we go in the investigation of mat- 

 ters of this character, the more we are thrown back upon 

 hypothesis, and the wider will be found the differences be- 

 tween the theories of different investigators. For example, 

 you will note at the outset two diverse theories of the con- 

 stitution of what we call matter ; one, that it consists of ex- 

 tremely minute particles or atoms, separated from each other, 

 and in constant agitation ; the other, that these atoms are 

 themselves simply vortices, or centers of a peculiar motion. 



(And perhaps I had better state thus early that this essay 

 must of necessity be an almost inextricable tangle of fact 

 and hypothesis. In many directions we are merely guessing 

 the unknown from the known, and you will doubtless find 

 that I have mingled my own guesses with those of others. I 

 have simply, to the best of my ability, tried to indicate what 



