Chap. 10.] affumes the Form of a Bow. 281 



a particular colour. When the plane H M W A is 

 perpendicular to the horizon, the line M W is di- 

 rected to the vertejc of the bow, and W K is its alti- 

 tude. 



Hence the problem is reduced to a quefticn to find two angles 

 whofe fines and tangents fhall be to each pther in a given ratio. 

 Let *:=cof. of A. 

 = cof. of B, 



== Tan. A. 



K 



Hence the co-fine of one angle being found, its fine is given, and 

 from thence the fine of the other angle, fince they are in a given 

 ratio to each other. 



Thus, according to the nature of the bow, whether primary, 

 fecondary, &c. the greatcft angle between the incident and emer- 

 gent rays is found ; but in this cafe the rays entering juft above 

 or below the point where the incident ray makes the greateft angle 

 between the incident and emergent rays muft, after emerging from 

 the drop, proceed nearly parallel to each other, and confequently 

 a number of rays of one colour will fall upon the eye, diverging 

 from the point where the angle between the incident and emer- 

 gent rays is the greateft, and produce the appearance of that co- 

 lour at the thus, determined height in the Ikies. 



This 



