326 A TREATISE 



red: and their mixture on the other fide,where the light is wea- 

 kelr, will make a violet or blew : and this we fee to tall cut ac- 

 cordingly , in the light which is dueled by going through a 

 prifme ; for a red colour appeareth on that fide from which the 

 light doth diiarc or encreafe , and a blew is on that fide towards 

 which it decreafeth. 



Now if a darke body be p'aced within this light/o as to have 

 the light come on both tides of it : we fhall fee ihc contrary 

 happen ahout the borders of the picture or iliadow of ue darkc 

 body : that is to lay, the red colour will be on that fide of the 

 pidure which is towards or over againfl the blew colour ti,at is 

 made by the glafle : and the blew of the picture will beontkat 

 fide which is towards the red that is made by rhc gJafte , as you 

 may experience if youp'acca fknderopacour body a'ongthc 

 prifrne in t!je way of n,c .'igijt either before or behind the 

 prilme. The rcaion whereof is t; .at the opacous body /landing 

 in the middle. environed by ii^tn ,.!:ud:-ii. ti,e 'i^nt.andmaketh 

 two lights of that which was bur M--C : each of which lights 3 is 

 comprifed between twodarkneflcs, fo wit, between each border 

 of fliadow that joyneth to each exiream of the light that comcth 

 from the glaffe, and each fide of theopacous bodies /hadovy. 

 Wherefore, in each of theie lighcsjor rather in each of their com^. 

 mixtions with darkncfle, there mutt be red on the one fide, and 

 blew on the other; according to the courfe of light which we 

 "have explicated. 



And thus it frlleth out, agreeable to the rule we have given, 

 that blew commeth to be on that fide of the opacous bodies fha- 

 dow on which the glaffe cafteth red, and red on that fide of it-on 

 which theglaflecafleth blew: likewise when light going through 

 a convexeglafle maketh two cones , the edges of the cone be- 

 twixt theglaffe and the point of concur fe will appeare red, ii t':e 

 roome be darke enough : and the edges of the further core, will 

 appcarcblew, both for the reafon given 4 : for in this^cafc the 

 point of concoarfc is the firong light betwixt the two cones : 

 f which , that betwixt theglafTc and the point, is the flrorger., 

 that bcynd the point the weaker : and for this very reafbn , f 

 a* opacous body be put in the axis of theie two cones . both rhc 

 fides of its picture will be red, if it beheld in the firft ccne which 

 is next to the glafle^and both will be blcrv ifthe body be Ctuated 



a 



