Mifcellanea Curia fa. 3 3 



fcrib'd on the Center C with the Radius CD? 

 which is to AC, in the given Proport'-m of 

 the Refra&ion : I fay then that the Lines 



AB, Ab, A3, Av, will make with the Line 



AC, the Angles CAB, CAb, C A3, €Av, equal 

 to the Refracted Angles ; and with the re- 

 fpeftive Rayes CB, Cb, C3, Cv, they will 

 make Angles equal to the Angles of" Inci- 

 dence that are required ; viz.. ABC (or ra- 

 ther its complement to a Semicircle) for the 

 Primary Iris, AbC, for the Secondary, A0C, 

 for a Third Iris, AvC, for a Fourth, If any 

 one has a mind, to find thefe Angles by an 

 accurate Calculation, 'twill follow from the 

 fame Principle, that putting- the Radius =1^ 

 and the Ratio of the Refra&ion as r to s, the 



Sine of Incidence will be ^ — IIL and the 



3 S*, 



Sine of the Refrafted Angle V V* _ Lf rom 



3 rr 3 j 



Which Angles proceeds the Primary Iris. For 

 th e Second ary the Sine of Incidence will be 

 n/ 9 irr 



8 2s7 7 the Sine of the Refrafted 



a 1 v 9 SS 1 



g Sr7~ 87 For a r/?/r ^ /r ^ the Sine 



of Incidence will be lrr - and the Sine 



of the Refrafted Angle ^ — 



I $rr 15 



For a 



Fourth 



