342. Matter is a tension of light that has become central. This continuous tension of light in matter in relation to the centre, and thus with curvation, is called _Refraction_.
343. All transparent bodies must refract light. The bodies are, however, denser than the æther; therefore the light, which passes from a rarer into a denser medium, must be refracted towards the centre (plummet of incidence), and in the reverse case turned from it.
344. Materiality is not the only determinant of refraction, but also the density of the element, the earth refracting light more than water, and this more than air.
345. The density also is not the only determinant, but the quality also of the matter; the Basic or Planetary must refract more than the Oxygenic or Solar.
346. As translucency is not a dead transmission of light, but a continued propagation of tension; so must it be viewed as a process of light in matter, but one excited from without. Translucency is a _co-illumination_, like the concord of equally attuned instruments.
347. Co-illuminating bodies are thus analogous still to the æther. If there are non-transparent bodies, they can only be found in the earth-element, which, being furthest removed from the æther, has perfected itself independently, and they must indeed be wholly deoxydised.
348. The co-illumination of bodies or their transparency is an effort of deoxydation. Bodies that cannot at all be deoxydised are non-transparent.
349. Transparency belongs only to those bodies which have in themselves a twofold character. It will be shown that the metals are absolutely identical matters, and therefore non-transparent. The metals are the only non-transparent bodies. Metaleity = non-transparency.
350. The light falls upon a non-transparent only through a transparent body, and thus one in which the tension of light propagates itself. This co-illumination of the matter placed in front of the non-transparent body cannot cease to co-illuminate; the tension must thus abide in it, and turn back from the non-transparent body, in a straight direction if the tension fell direct upon it, at a certain angle, if obliquely. This phenomenon is called _Reflexion_.
351. Reflexion is no repulsion of light, but only its tension continued into the medium, in which the tension has been.