I will not delay you by any defence of the arrangement of sciences I have chosen. Of course we may at once dismiss chemistry and pure mathematics from our consideration. Chemistry can do nothing for art but mix her colours, and tell her what stones will stand weather; (I wish, at this day, she did as much;) and with pure mathematics we have nothing whatever to do; nor can that abstract form of high mathesis stoop to comprehend the simplicity of art. To a first wrangler at Cambridge, under the present conditions of his trial, statues will necessarily be stone dolls, and imaginative work unintelligible. We have, then, in true fellowship with art, only the sciences of light and form, (optics and geometry). If you will take the first syllable of the word 'geometry' to mean earth in the form of flesh, as well as of clay, the two words sum every science that regards graphic art, or of which graphic art can represent the conclusions. 97. To-day we are to speak of optics, the science of seeing;--of that power, whatever it may be, which (by Plato's definition), "through the eyes, manifests colour to us." Hold that definition always, and remember that 'light' means accurately the power that affects the eyes of animals with the sensation proper to them. The study of the effect of light on nitrate of silver is chemistry, not optics; and what is light to _us_ may indeed shine on a stone; but is not light to the stone. The "fiat lux" of creation is, therefore, in the deep sense of it, "fiat anima." We cannot say that it is merely "fiat oculus," for the effect of light on living organism, even when sightless, cannot be separated from its influence on sight. A plant consists essentially of two parts, root and leaf: the leaf by nature seeks light, the root by nature seeks darkness: it is not warmth or cold, but essentially light and shade, which are to them, as to us, the appointed conditions of existence. 98. And you are to remember still more distinctly that the words "fiat lux" mean indeed "fiat anima," because even the power of the eye itself, as such, is _in_ its animation. You do not see _with_ the lens of the eye. You see _through_ that, and by means of that, but you see with the soul of the eye.