'With regard to the most interesting of all their [the philosophers'] modes of force-light; they never consider how far the existence of it depends on the putting of certain vitreous and nervous substances into the formal arrangement which we call an eye. The German philosophers began the attack, long ago, on the other side, by telling us there was no such thing as light at all, unless we choose to see it.² Now, German and English, both, have reversed their engines, and insist that light would be exactly the same light that it is, though nobody could ever see it. The fact being that the force must be there, and the eye there, and 'light' means the effect of the one on the other - and perhaps, also - (Plato saw farther into that mystery than anyone has since, that I know of) - on something a little way within the eyes.'