Chap, r 3. eXTfiM^/ttf/'BODIES. 159 



Thirdly,in this explication it would alwaycs go one way iti 

 theaire,and another way in the glafTe: whereas nil experience te- 

 ftificth, that in a glaffe convex on both fides, it ftill goeth in the 

 aire after its going out to the fame fide as it did in the glaflejbuc 

 more. And the like happencth in glafles on both fides concave. 

 Wherefore it is evidcnt>that it is the fuperficies oftheglafle that 

 is the worker on both ficfes; and not the fubftance of the aire on 

 the one fide, and of the glafle on the other. 



And laftly, his anfvver doth no way folve our objection, 

 Which proveth that the refiftance both wayci is proportionate 

 to the force that moveth,and by confequence that the thing mo- 

 ved muft go ftraight.As we may imagine would happen if a bul- 

 let were (hot Hoping through a green mud wall, in which there 

 were many round Hicks fo thin fet that the bullet might pafTe 

 with eafe through them;for as long as the bullet touched none of 

 them ("which cxprefleth his cafe) it would go ftraight; but if it 

 touched any of them ( which refcmblctli ours, as by and by 

 will appear) it would glance according to the quality of 1 the 

 touch, and move from the ftick in another line. 



Some peradventure may anfvver fop MonnVur DCS Cartes that 

 this fubtile body which hefuppofcth to tun through all things is 

 ftiffe and no wayes pliable. But that it fo repugnant to the na- 

 ture of rarity & fo many infuperable inconvtniencies do follo\v 

 out of it; as I cannot imagine he will own te ; and therefore I 

 will not fpend any time in replying thereunto. 



We muft therefore feck fome other taiife bf the refraction of 7. 

 light, which is made at the entrance of k mtr* diaphanous bo- ^ truecaufe^ 

 dy. Which is plainly ("as we fa-rd before) b<Scaufc the *ay (hi- light both a" 

 &in aeainft tlic infidc ofa body it carmot penetrate, turnttlvby _entrance, & 



rt f i ii J L. c ' c *S OIn 8 out 



reflexion towards thatfide on which the ilhimuia-Ht [tandctn: fi-omtheicHc- 

 and ific findeth clear paflage through the Whole refirtent,k fbl- ft 

 loweth the coitrfc it firft taketh; if not, ihcil it is loft by many 

 reflexions to and fro. 



And- that this do6r,n4i is true, the accidcrtts or Phenometm 

 evidently declare unto us; for experience teathcth us, that upon 

 a plain fuperficies the refraction is made towards the penpendi- 

 cular drawn from the illuminant to the fuperficies ; as we have 

 fnkt. Now at the going out ( if the furfaces be parallels ) we fee 

 that the ray turnetli from that perpendicular; which aifo is ne- 



ccflary:. 



