A Trttlifecf BODI 



ES. 



rom it ; 

 when the fc- 



Chap, t j. 



kind of Reflexion : for there being certain bodies, in which thd toward . 

 paffages are fo well ordered with their re/iftances, that all the 

 prtrtsofthem feemtfrpe'rmrt light ropafle through thcm.arrdyet 

 al! part* of them feem to reflet it ; when light paffeth throtrgh c Jn d r u perfic : et 

 fuch bodies, it findeth at the* very entrance of them, fuch reh- is P ara ' Icl " 

 frances where it pattern, as fcrfe it for a reffe$ent body; nnd yet 

 fuch a rcfle<5rerrt body^s hirrderetn not the pifldge through; but 

 onelyhindereth the 1 paffage from being in* frtaight line with the 

 lint incident. Wherefore trie light mutt needs take a ply ai beaten 

 from thofe parts towards a line drawn from the ifluminant, fal- 

 ling perpendicularly rrpo-rf the refitting fuperficies; and therefore 

 is termed by mathematierarrs,to be- reflated of broken toi^ards 

 thcperpendicular.Now at the very going out again of the fight, 

 the fecond ftiperffciejC if it be parallel to the former ) muf! rteeds 

 upon a c6ntrJty caule, ftfike if the contrary waV: U-hich is 

 termed from tfcc ptrpendicular. 



As for example: 

 rf the ray A B, 

 lighteth upon the 

 fuperfTcres ^ B F, 

 and findeth en- 

 trarrcc * it h not 

 riOAv the fuperfi- 

 cits E F, that re- 

 fifteth or reflecl- 

 eth rt:bnt it is that 

 part of the hifide 



("as we may fay)of cfrc pore B,wh?ch Is towards Fjaitd is a Phy- 

 ficnll body, not a Matnematrcall pornt. The refletiort therefore 

 mnft be made, as if the refleftent body were I B K! but it is evi- 

 dent that if A B, did ftrike upo:r JK,it would reflect rowdrrfs 

 A G. But becaufe we know not the inclination of the fuperficies 

 I K, whether it be truly a perpendicular or no , therefore we 

 cannor tell the quantity of the inclination which this reflefcfon 

 muft make; but onely we know that it rmift be towards- A G. 



But before we wade any deeper irrro this din5curty,we cannot f 5\ 

 omit a word of the manner of explicating refraction which Mon^ei' r 

 Monfieur Des Cartes ufcth,fo witty a one as I am forry it wanr- Cartesh 

 eth fuccefle. He therefore following the deffidnftraticm above " 



Id. ' 



G 



