292 Mr. Ainger on the 



produce the comparative darkness in question, it may be noticed 

 that the violet edge of the bow is extremely ill defined as con- 

 trasted with the red edge. In some cases, the colour can with 

 difficulty be traced beyond an indistinct green, the remainder 

 seeming to be merely the commencement of the blue colour of 

 the atmosphere. According to the descriptions usually given, this 

 difference would not exist ; the parallel emergence of the violet 

 rays ought to produce a very distinct line of violet light, 

 because the red and yellow rays are in that situation subject 

 to considerable divergence. But the fact is, that notwithstand- 

 ing their divergence, they are far from imperceptible ; and, 

 mixing with the parallel violet rays, they confound and almost 

 obliterate them, or rather unite with them to produce the 

 impression of common compound light. 



The superior brilliancy of the primary bow is not, I think, 

 quite accurately accounted for when it is ascribed to the cir- 

 cumstance of its rays having suffered but one reflexion ; for 

 the double reflexions are made at angles so favourable, as 

 nearly to counterbalance this difference. I apprehend that the 

 faintness in the latter case is owing to the following causes : 



1. That the rays which suffer the maximum deviation in the 

 primary bow arrive at the surface under a much smaller angle 

 of incidence than those which suffer the minimum deviation 

 in the secondary bow ; the latter, therefore, are more copiously 

 reflected from the first surface, and enter the drop in much 

 smaller quantities. 



2. That the angle at which the ray is afterwards refracted 

 from the inner surface to the air, is, in the secondary bow, 

 similarly favourable to reflexion, and unfavourable to refrac- 

 tion, so that only a small portion of the already reduced quan- 

 tity of admitted light is refracted. 



3. That the extent of the dispersion is increased by the 

 second reflexion, as is shewn by the greater width of the 

 secondary bow. 



The last circumstance may, perhaps, be considered as 

 included in the expression that the faintness is owing to the 

 second reflexion, though it is not very obvious that such is 

 the meaning. 



