152 Mr potter, on THE PROBLEM OF THE RAINBOW, &c. 



the higher and lower parts of the cloud, they must come in contact, 

 and gradually form large drops, and thus their diameters become at 

 length too, great to give an appearance of supernumerary bows. There 

 are other points still, however, which theory wiU guide us to look 

 for in future; thus if the drops are larger, the second maximum of 

 the red may happen in the green's place, and thus the green be di- 

 luted with white light whilst the orange and yellow would be briUiant, 

 but the second maxima of these latter falling in the blue and purple, 

 these colours would again be diluted. In such bows the red, orange 

 and yellow, would form the most striking part. I am not aware that 

 there are any recorded observations relating to this or similar effects. 



If we can judge by observation where the second series of maxima 

 commence, we shall be able to calculate the size of the drops forming 

 the bow. 



There are observations on record of supernumerary bows attending 

 the secondary rainbow : their solution is perfectly similar to the one 

 given for the primary one. 



The comparison of the results of interference with the common 



explanation of the rainbow, required that the plan followed should be 



in accordance with the undulatory theory of light. If the effects were 



considered to be those due to a difference of ^ an interval in the paths 



of the rays at the cusp, the results would be similar, only modified 



a little in quantity. 



4 

 I have also taken, as ordinarily is done, that fi = - for red rays, 



although Fraunhofer's observations shew it to belong to the letter D, 

 nearly, and the middle of the orange. 



Again, I have taken the interval X, as given from Sir Isaac -Newton's 

 measures, although luipublished measures of my own confirm those of 

 M. Fresnel in shewing that they are somewhat too small. 



