JVIifcellanea Curiofa. 29 



Now this greAteft Excefs doubled, is always 

 the Diftance of the fyk from the Point oppojite 

 to the Sun, when the Number of Reflexions is 

 uneven. But if that Number be even, then the 

 Double of that greatefl Angle, is the Diftance 

 of the Iris from "the Sun it [elf, viz. in the 2d, 

 4th, 5th, &c. Iris. All thefe Things are ei- 

 ther purely Cartepms, or elfe eafily follow 

 from his Writings in the foremention'd Place. 



But now to obtain thofe great eft Exceffes, 

 having the Refradion of any Liquor given 9 

 'tis to be obferv'd, that the Excefs of Two 

 refraded Angles, above one of Incidence, is 

 there the Greateft, where the momentaneom In- 

 crement of the Angle of Incidence is exadly 

 double of the mome?2taneons Increment of the re- 

 fraded Angle. And that the Excefs of Three 

 refraded Angles is there the Greateft, where 

 the Increment of the Angle of Incidence is 

 triple the Increment of the refraded Angle - T 

 and fo of the reft. And this is fufficientiy 

 evident of itfelf: But as for the Angles, we 

 may obtain them by the Help of the following 

 Lemma, which muft therefore be demonftra- 

 ted. 



LlM- 



