QVEST. XXXI. Of the difference betwixt Lux or Light it selfe, and Lumen or Illumination.
THose which do peremptorily persist in the defence of the intentionall or imaginary essence of light, hold that Lumen or the Illumination and en∣lightning is a species or kinde of that we call Lux or the Light. For, as the colour and the species do differ in kinde, so in like manner dooth the light it selfe differ from the Lumen or enlightning, because as colours by their species becomme sensible, so the light is seene by the illumination of it as by his species or forme. But we consent not with them: for if light were seene by illumination, then this illumination would not fall vnder the Sense; for the species of sensible thinges are not themselues perceiued but they are that whereby the obiects do moue the Sense; seeing then the Lumen is seen by it selfe it cannot be that the Light should through it at∣taine vnto the Sense.
But they further obiect, that the Lumen or enlightning is in a tralucent bodie, and the light or Lux in a darke bodie, and that therefore they differ in specie or in kinde one from another. But I answere that it is not so; indeede we grant that the Lumen is in a tralucent or bright bodie, but we confidently denie that the light is in a darke bodie, for it is also in a tralucent body, yet in a subiect more dense and darke then that of the Lumen, for the light it selfe is more darke then the illumination: therefore saith Arist. it doth determine or limit the sight, whence it hath the name of a colour. For hee calleth light white in the booke De sensu & sensili, and also in the fourth chapter of his first booke of Meteors hee calleth the Sun white. But the matter is cleere of it self, for we perceiue that our sight is terminated in a flame, in the Sun, or in the Moon, neither are any other colours brought vnto vs through them.
But it may be obiected that light seemeth to be permanent and abiding in the sub∣iect, but the Lumen is not except in some cleare, bright body. I aunswere it is true, but yet this doth not argue a specificall difference: for as the heate being proper vnto the fire doth abide therein, and the other heate which is produced from this dooth vanish when the fire is remooued from it, yet they differ not in kinde, so neither doth Lumen or enlightening differ from Lux or the fountaine of this Illumination.
But there be many reasons why they do not differ in kind one from another. For some∣time the Lumen or illumination dooth assume to it selfe the nature of Lux or Light. So the Moone hath light which is manifestlye nothing else but the very enlightning of the Sun. But do they not at all then differ? I say they differ, yet in the Planets not truely but onely in respect. For example, the Moone as it doth enlighten the earth hath Light, but as it receyueth this light from the Sun it is onely an illumination; and hence it is that some illumination hauing a conuenient dark body opposed to it will becom light & send an illumination out of it selfe: But if you let it bee without a darke body it will be onely an illumination. Euen as the Elementary fire in his proper place is commonlye called Lumen and yet is not seene because it hath no darke body, that so it may transmit her il∣lumination to vs, so that light is no other thing but a condensed illumination, yet not so that it doth degenerate into a colour.
Moreouer, they differ in the subiect. For this Lumen or illumination in his proper sub∣iect is Lux, that is, a Light; but being without it, it is a meere illumination, that is, Light is properly called that which is in a lucide or bright bodie, as in the Sunne and in other Starres; but illumination is that which is produced from the light, so that in the sun there is not illumination but light, and in the aire there is no light but Lumen or illumination onely.