the Cause of coloured concentric Rings. 291 
which it follows, that streaky appearances must every where 
be seen in the composition of the rays that come to the eye. 
We should also notice that towards $ all colours but violet will 
be transmitted, for which reason when they rise again a com- 
pound of them will produce streaks that approach to white, 
such as pale red, pale bluish green, dingy yellow, and dirty 
white ; so that both at the beginning and end of the bow- 
streaks all observations * of them agree perfectly with what 
is pointed out by the foregoing remarks ; and though we have 
not analysed the particular construction of the streaks in the 
middle of the bow, yet what has been said will sufficiently 
prove that various successive changes of the colours must also 
take place. 
It will be understood that I have only attempted to give 
some idea of the action of surfaces, in giving configuration to 
colours that are already produced ; but that the principle of 
reflection is the cause of streaks will remain evident, even if 
the method of its action should not have been explained so 
much to our satisfaction as we might wish. It will also re- 
main to be proved, that streaks are only the effect of one of 
those modications which depend on the figure of the reflect- 
ing surface ;-f and having got thus far in this research, I may 
advance towards a final consideration of my subject. 
49. Prismatic Bows when seen at a Distance are straight Lines . 
The next point to be shown, in order to approach gradually 
to a solution of my problem, is that the apparently arched 
figure of the blue and red bows, which may be seen in a prism, 
* See the first paragraph of the last article, 
f See the second paragraph of the 44th article. 
