3 i7 A TREATISE 



that, where light is not^darkenefle is ; then confider, that light 

 being diverfly to bcecaft, but efpecially , through or from a 

 tranlparent body , into which it finketh in part. and in part it doth 

 not : and you will conclude, that it cannot chooie but come out 

 from liich a body , in divers forts mingled with darkenefle : 

 which if it bee in a lenfible quantity, doth accordingly make 

 divers appearances : and thole appearances mull of neceflity 

 have divers hues ., reprefenting the colours which are middle 

 colours betweene white and black ; fince whire is the colour of 

 light, and darkeneffe ieemeth black. Thus , thole colours are 

 ingendred, which are callecfapparent ones. And they appeare 

 ibmetimes but in fome one pofition ; as in the rainebow ; which 

 chan^eth place as the looker en doth : but at other times., they 

 may DCC leen from any part ; as thofe which light maketh by a 

 double refraction through a triangular glafle 



And that this is rightly delivered , may be gathered out of 

 the conditions requifite to their production : for that cryftall, or 

 water , or any refracting body , doth not admit light in all its 

 parts, is evident, by reafbnof the reflection that itmaketh, 

 which is exceeding great : and not onely from the fuperficies, 

 but even from the middle of the body within : as you may fee 

 plainly, if you put it in a darke p!ace,and enlighten but one part 

 of it : for then, you may perceive, as it were, a current of light 

 pafle quite through the body , although your eye be not op- 

 pofite to the paflage: fb that,manifeftly it reflefteth to your eye 3 

 from all the inward parts which it Jighteth upon. 



Now a more oblique reflection or refraction dcth more dip 

 psrfe the light, and admitteth more privations of light in its 

 parts,then a lefle oblique one : as Galileo hath demonrtrated in 

 the firft Dialogue ofhis lyfteme. Wherefore, a lefle oMique re- 

 flection or refratfion 3 may receive that in quality of light,which 

 a more oblique one maketh appeare mingled with darkeneffe ; 

 andconfequently, the fame thing will appeare colour in one, 

 which flieweth it felfe plaine light in the other ; for the greater 

 the inclination of an angle is , the greater alfb is the di/perfion 

 of the light. 



And as colours arc made in this fort,by the medium through 

 nhich light pafleth, fo ifwe conceive the fuperficiei from which 

 the light refkaeth, to bedivecfly ordered in refpeft of reflexi- 



on. 



