342" On Halos, 



tween MA and MF will be refleftcd by the 



furface FD; for, rad. : S of the angle CBF : : C B 



: CF : : CB : CD (BD being the direftion 



of MB after refraftion) : : S. of the angle 



CDB : S. of the angle CBD : : S. of the angle 



EDB : S.ofthe angle CBD :: S.of the angle CBF 



=«= rad. X S. of the angle CBD , a c v. i 

 2 but S.ofthe angle 



S.of the angle EDB ° 



CBF : S. of the angle CBD : : S. of incid. : S. of 



e CL -, rad. X S.ofthe angle CBD . o c 



rcfraa. hence >_ — _.; t-^^^-jt^^ — • S. of 



S. ot the angle EDB 



the angle CBD : : S. of incid. : S. of refraft. or 



rad. * S. of the angle EDB : : S. of incid. : S. of 



refradt. Confequently, the angle EDB is the leaft 



angle of incidence on the fecond furface that the 



rays can have, and be reflefted. 



Thefe rays will be emergent in different di- 

 redtions, and the nearer they are to MB (fig. 3.) 

 the lefs will be the inclination of thofe in the 

 fame pencil to each other and to GO. Hence it 

 appears that the lefs refrangible rays will be 

 nearly parallel to the more refrangible effedlual 

 rays which come from the fame drop, and by a 

 mixture of the different colours, may be pro- 

 duced the whitenefs in the interior part of the 

 firft halo. Thefe rays will be too much difperfed 

 to produce any eflPeft in the fecond and third. 



It may eafily be conceived, from the manner in 

 which Sir Ifaac Newton has expreffed himfelf, 

 that had the diameters of the halos he mentions 



been 



