Perhaps, however, instead of leading to a "triumph of Idealism," the paradoxes and incongruities--in a word, the vast accumulation of the Unknowable--belonging to eyesight _considered as a Sensation_, must be allowed to land us on the shore of a far-stretching Scepticism illimitable to the mind's eye. And this seems to be the eminent writer's own final opinion.[123] So, too, it will always appear when the case is fairly argued out; and that for the reasons adduced in our text. The course of argument there pursued was adopted before the Professor's book came to hand; but we have now added some extracts from his pages in the shape of footnotes, and have given references to other interesting topics touched upon by him. For our purpose, however, it is necessary in some degree to disregard the variety of those topics, and fix our attention upon the conclusive issue. It is plain, that respecting our senses, as well as our other primary sources of information, the limits of what we can completely explain are very narrow. Yet each for himself and all of us for our race must needs every day accept and act upon this limited and imperfect kind of knowledge about what most essentially concerns our actions as well as our speculations. Several strong examples of such incompleteness are given by Helmholtz in his scientific inquiry into the rationale of the visual sense-impressions. We observe, for instance, in his chapter on Sensation (p. 236 seq.) that all light-waves are the same in kind of movement, but differ in size as widely as the ripples on a sea-beach (round which happy children play) differ from the vast Atlantic ship-engulfing billows sixty or a hundred feet apart. All these undulations are similar in respect of reflection, refraction, interference, diffraction, and polarisation, as well as in their production of heat.[124] Now, it is the interpretation of such movements into its own language by which our eye gives us the sensation of colour. Yet this power of interpretation is curiously limited--it does not appreciate the gentler ripples of the light-waves--it does not reach to their mightier undulations. Consequently, there may be tender colour-delicacies adorning the Universe, completely incognisable by us, and there may be also glows and intensities of light-beams magnificently resplendent, and unspeakably grand in tone, of which we can through our visual apparatus form no possible conception. Thus, our eye translates some waves into a language which we call colour, but its scholarship is limited. A certain number of signs it catches and interprets, the rest lie altogether outside its ken. The Sun's softer light-harmonies, and his most awful emanations of beauty remain equally unknown.