CHAP. 2. 20. CAUSE OF THE HALO, &c. 109 



manner. A double Corona, the inner one of which 

 is 5 diameter, and the outer 10, is referrible to 

 a property in the cloud of refracting certain of 

 the rays at every angle, from \" to 2 30', and 

 certain other rays, from 2 30' to 5, and so on 

 of triple ones.* 



For further particulars relative to these 

 phaenomena, I refer the reader to the works of 

 Aristotle,f Newton,! Huygens,|| Des Cartes, $ 

 M. Helvetius,^| and to several papers in the 

 Philosophical Transactions** and Manchester's 

 Memoires.ft For explanation of the phaeno- 

 mena of the Rainbow, consult Newton's 

 Op ticks. 



By the problem above it appears, that no 

 two persons standing at any distance from each 



* Even the breadth of the ring of a Halo itself must be 

 caused by a number of rays, refracted at somewhat different 

 angles ; otherwise the breadth of the ring would equal only 

 the breadth of one ray. 



t Aristot. Meteor, lib. iii. cc. 8, 4, 5, 6. 



$ Newton, Optic. 1st edit. 2d book, pp. 48. 134. 



|| Huygens's Post. Works, pp. 293. 



Des Cartes. Treatise of Meteors. 



IF M. Helvetius. End of Mercurius in Sole. 



** Phil. Trans, vol. v. 1065. xxii. 535. xxxi. 212. xxxix. 

 218. xlvi. 196. Iii. 3. 



ft Manchest. Mem. vol iii. 



