[Book III, 



CHAP. X. 



OF THE RAINBOW, AND OTHER REMARK- 

 ABLE PHENOMENA OF LIGHT. 



Gf the primary and fecondary Rainbow. Why the Phenomenon affumci 

 the Form of an Arch. At what Angles the different Colours are 

 apparent. Lunar Rainbow. Marine BO~M. Coloured Bowsfeen 

 n the Ground.-*- Halo or Corona. Curious Phenomena fsen on the 

 I~ 6 P of the Cordileras. Similar Appearance in Scotland. Parhelia, 

 or Mock Suns. Singular Lunar Phenomenon.' Blue Colour of the 

 .Atmofphere. Red- Colour of the Morning and Evening Clouds. 

 Colour of the Sea. 



SINCE the rays of light are found to be decom- 

 pounded by refracting furfaces, \ve can no longer 

 be furprifed at the changes produced in any object by 

 the intervention of another. The vivid colours, 

 which gild the rifing or the fetting fun, mufl necef- 

 farily differ from thofe which adorn its noon-day 

 fplendor. There muft be the greateft variety which 

 the livelieft fancy can imagine. The clouds will 

 afiume the moll fantaftic forms, or will lour with the 

 darkeft hues, according to the different rays which 

 are reflected to our eyes, or the quantity abforbed 

 by the vapours in the air. The ignorant multitude 

 will neceflarily be alarmed by the fights in the hea- 

 vens, by the appearance at one time of three, at ano- 

 ther of five funs, of circles of various magnitudes 

 round the fun or moon, and thence conceive that 

 fome fatal change muft take place in the phyfical or 

 the moral world, fome fall of empires or tremendous 

 earthquake, while the optician contemplates them 



merely 



