150 Mr potter, ON THE PROBLEM OF THE RAINBOW, 



Finding the two values of (p, the one above and the other below the 

 ano-le of minimum deviation for this value of «, and then deducing those 

 corresponding for p and 0, I find 



^ = 50\ p = l.96imr, e=-lT. 16». 33", 



<p = 6T.55\ p = 1.272036»-, 6= 92°. 58'. 31", 



rt,= .8996004r, *, = .8993300/-, 

 «,= 1.781031 »•, *, = .8213489r. 



Applying these to the above expression, we find 



j<'-M = .0036783r, 



and that the second maximum of the red may occur at the place of 

 the first violet, we must have, if X be the interval of the luminiferous 

 surfaces for red light, 



1,' -u=\ = .0000256 inch, 



and the diameter of the drop = 2r, 



■0000256 

 ~ .0036783 



= — - inch nearly, 



72 



which does not differ greatly from Dr Young's result ;^, for I have 

 taken a = 1° . 46', and he has taken it = 2°. 



We see also that if /• were very small, as in mist and in ordi- 

 nary clouds not producing rain, probably much less than ^^"' of an 

 inch, then the primary red would extend far beyond the violet's place, 

 and so likewise with the other colours, and we ought to expect a bow 

 with colour scarcely perceptible, and such is recorded as the fact. 



In the case calculated the primary pui-ple mixing with the second 

 red would give a reddish purple, which agrees with an observation I 

 made on a very splendid display on the 5th of June 1834, immedi- 

 ately after a heavy thunder-shower. I saw three sets of purples at the 



