280 



PROFESSOR MILLER, ON SPURIOUS RAINBOWS. 



distances of as many of the dark bars as could be conveniently observed, 

 are given in order to meet any future calculation of their places. The 

 observations of the points at which the bows appeared to commence, 

 present, as might be expected, great discrepancies ; they shew, however, 

 that in every case the illumination extends considerably beyond the place 

 of the geometrical bow. The spectrum seen through the red glass fades 

 much more abruptly from its brightest point towards the more refrangible 

 end than towards the less refrangible end. JV being the more refrangible 

 end, M the brightest point, L that at which it begins to fade, K the 

 least refrangible end ; the indices of those points deduced from the 

 double deviations through a hollow prism having an angle of 66°.22' are, 

 at K 1.3294, at L 1.3310, at M 1.3322, at N 1.3334. The best single 

 equivalent index will probably be about 1.3318. 



(A) 



Primary bow, seen through red glass, for which it has been assumed 

 that n = 1.3318, and .-. 4 ■$' — 2 cf> = 42°.15'. Diameter of the cylinder of 

 water = 0.0206 inch. 



