336 



WELLS'S NATURAL PHILOSOPHY. 



How is the 

 ])rimary rain- 

 bow formed '! 



Fig. 271. 



Fig. 272. 



The inner, or primary rainbow, wliicli is the 

 one ordinarily seen, is formed by two refrac- 

 tions of the solar ray, and one reflection, the 



ray of light entering the drops 



at the top, and being reflected to 



the eye from the bottom. 



Thus, in Fig. 271, the ray S A of the pri- 

 mary rainbow strikes the drop at A, is re- 

 fracted, or bent to B, the back part of tho 

 inner surface of the drop ; it is then reflected 

 to C, the lower part of the drop, when it is 

 refracted again, and so bent as to come di- 

 rectly to the eye of the spectator. 



Howisthc Bee- The secondary, or outer rainbow, is produced 



bow^fJrm/d?"" ^y t'^^'*^ refractions of the solar ray, and two 



reflections, the ray of light entering the drops 



at the bottom, and being reflected to the eye from the top. 



Thus, in Fig. 272, the ray S B of the sec- 

 ondary bow strikes the bottom of the drop 

 at B, is refracted to A, is then reflected to 

 C, is again reflected to D, when it is again 

 refracted or bent, till it reaches the eye of 

 the spectator. 



The position and formation of the primary 

 and secondary rainbows are represented in 

 Fig. 273. Thus, in the formation of the pri- 

 ^\ mary bow, the ray of light S strikes the drop 

 n at a, is refracted to b, reflected to g, and 

 leaving the drop at this point, is refracted 

 to the eye of tho spectator at 0. In the formation of the secondary bow, 

 the ray S' strikes the drop p at the bottom at the point t, is refracted to d, 

 reflected to /, and thence to e, and refracted from the top of the drop, pro- 

 ceeds to the eye of the spectator at 0. 



Tho reason the outer bow is paler than the inner is because it is formed by 

 rays which have undergone a second internal reflection, and after every re- 

 flection light becomes weaker. 



wiiat are Halos are colored rays which are sometimes 



iiaios? gggjj surrounding luminous bodies, especially 



the sun and moon. They are occasioned by the refraction 

 and decomposition of light by particles of moisture, or 

 crystals of ice floating in the higher regions of the atmos- 

 phere, and are neyer seen when the sky is perfectly clear. 



