337. Light, as an Ætherial, permeates matter, and must on that very account pass toward the middle point of the earth, because it is virtually none other than the tension of both middle points, the earth and the sun. Originally therefore the light must have gone through the earth.
338. This permeation is not, however, mechanical but dynamic, and is indeed necessarily a propagation of the tension of æther through the matter.
339. Matter is susceptible of the same polarization of which the æther is susceptible, because it is on no account different from the æther; the polarization only takes place more slowly.
340. The transmission of light is called Translucency.
341. The æther is transparent, because it is everywhere the propagation of the tension of light, because it is itself, or becomes, light everywhere. Bodies can also be transparent, only in so far as they are the light itself, i. e. in so far as the same polarization can be excited in them which is constantly excited in æther by the sun. But this is not only possible, but necessary; for matter is surely the æther itself, only condensed. The polarity æther must therefore be capable also of being excited in the condensed æther, although in a much less degree. The transparency of matter is a tension of æther continually ringing through matter. The whole universe originally was transparent; it has only originated through tension of light.
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.