computed, 



iOJinaXt, 



»7^ TWO INTEUSECTING RAINBOWS. 



the accidental rainbow muft have fomewhat participated- of 

 this indiftindnefs ♦. ■ 



The Inclination When phenomena of this kind occur, it would afford a Aire 

 ^<!mn^,fT^'" means of trying the juftnefs of the explanation, if the in- 

 clination of the two bows were obferved, and alfo the fun's 

 altitude at the fame time. Thefe two things are neceffarily 

 conneded ; for if we call I the angle of their interfe^tion, E 

 the elevation of the fun, and S the angle fubtended at the ey^ 

 by the femidiameter of the rainbow, if complete, an angle 

 which is conftantly the fame, and nearly equal to 42°, it is 



eafy to infer from fpherical trigonomelry,- that iln f I = ^' 



3*1 d was a little Computing from this formula, the inclination of the two 

 inore than the bows in the prefent inftance coines out nearly 5° ; fomewhat 

 greater than I was incimed to eftimate it by the eye. 



Phenomena of this kind can but rarely occur, as the necef- 

 fary conditions will not often come together. The principal 

 rainbow muft be over the fea ; the fea itfelf muft extend fome- 

 what on the fide toward the fun ; it muft be fmooth and 

 tranquil, and the fun fo low that the light retlefted from the 

 water may be confiderable. Were it ever to happen that the 

 accidental bow was completely formed ; the effed could not 

 fail to be very ftriking. 



* As th€ place of interjfeSion will lie in a plane palling througk 

 the eye of the obferver and parallel to the plane of refleftion ; does 

 not this faft afford ground for a fufpicion that the refleciion, at this 

 low altitude, was made, not from the furface of the fea, but from 

 that of the ttratum of vapour which occafions looming, and ha$ 

 been Co well treated of byDr. Wollafton and others, (fee our Jour- 

 nal, VJ. 46, and elfewhere), and that this ftratum was hrgher 

 farther out at fea than near the coaft ? — N. 



Nffikt 



