But when even such a primordial phenomenon is arrived at, the evil still is that we refuse to recognise it as such, that we still aim at something beyond, although it would become us to confess that we are arrived at the limits of experimental knowledge. Let the observer of nature suffer the primordial phenomenon to remain undisturbed in its beauty; let the philosopher admit it into his department, and he will find that important elementary facts are a worthier basis for further operations than insulated cases, opinions, and hypotheses.--Note M. [1] That is (according to the author's statement 150. 151.) both tend to red; the yellow deepening to orange as the comparatively dark medium is thickened before brightness; the blue deepening to violet as the light medium is thinned before darkness.--T. [Pg 74] XI. DIOPTRICAL COLOURS OF THE SECOND CLASS.--REFRACTION. 178. Dioptrical colours of both classes are closely connected, as will presently appear on a little examination. Those of the first class appeared through semi-transparent mediums, those of the second class will now appear through transparent mediums. But since every substance, however transparent, may be already considered to partake of the opposite quality (as every accumulation of a medium called transparent proves), so the near affinity of the two classes is sufficiently manifest. 179. We will, however, first consider transparent mediums abstractedly as such, as entirely free from any degree of opacity, and direct our whole attention to a phenomenon which here presents itself, and which is known by the name of refraction. 180. In treating of the physiological colours, we have already had occasion to vindicate what [Pg 75] were formerly called illusions of sight, as the active energies of the healthy and duly efficient eye (2), and we are now again invited to consider similar instances confirming the constancy of the laws of vision. 181. Throughout nature, as presented to the senses, everything depends on the relation which things bear to each other, but especially on the relation which man, the most important of these, bears to the rest. Hence the world divides itself into two parts, and the human being as _subject_, stands opposed to the _object_. Thus the practical man exhausts himself in the accumulation of facts, the thinker in speculation; each being called upon to sustain a conflict which admits of no peace and no decision. 182.