Chap. 10.] be Rainbow- 277 



merely as the natural and beautiful effects produced 

 by clouds or vapour in various mafTes upon the rays 

 of light. 



One of the mod beautiful and common of thefe ap- 

 pearances deferves particular inveftigation, as, when 

 this fubject is well underflood, there will be little dif- 

 ficulty in accounting for others of a fimilar nature, 

 dependant on the different refrangibility of the rays of 

 light. Frequently, when our backs are turned to the 

 fun, and there is a fhowc-r either around us, or at fome 

 diftance before us, a fpecies of bow is feen in the 

 air, adorned with all or fome of the feven primary co- 

 lours. The appearance of this bow, in poetical lan- 

 guage called the iris, and in common language the 

 RAINBOW, was an inexplicable myftery to the antients ; 

 and, though now well underftood, continues to be the 

 fubject of admiration to the peafant and the philo- 

 fopher. 



. We are 'indebted to Sir Ifaac Newton for the ex- 

 planation of this appearance, and by various eafy ex- 

 periments we may convince any man that his theory 

 is founded on truth. If a glafs globe is fufpended in 

 < the ftrong' light of the fun, it will be found to reflect 

 the different prifmatic colours exactly in proportion 

 to the pofition in which it is placed ; in other words, 

 agreeably to the angle which it forms wiih the fpec- 

 tator's eye and the incidence of the rays of light. 

 The fact is, that innumerable pencils of light fall upon 

 the furface of the globe, and each of thefe is feparated 

 as by a prifm. To make this matter (rill clearer, let 

 us fuppofe the circle B A W (Plate XXIII. Fig. 53.) 

 to reprefent the globe, or a drop of rain, for each drop 

 may- be confidered as a fmall globe of water. The 

 red rays, it is well known, are lead refrangible ; they 

 wiL therefore be refracted, agreeably to their angle of 

 incidence, to a certain point A in the moft diftant 

 T 3 



