262 HISTORY OF 



last bordered by a bright yellow, which altered into a straw 

 colour, and this tiuned to a green ; but, in all, the external 

 colour remained red." Such is the description of one of the 

 most beautiful illusions that has ever been seen in nature. This 

 alone seems to have combined all the splendours of optics in one 

 view. To understand the manner, therefore, how this pheno- 

 menon was produced, would require a perfect knowledge of op- 

 tics ; which it is not our present province to enter upon. It 

 will be sufficient, therefore, only to observe, that aU these ap- 

 pearances arise from the density of the cloud, together with its 

 uncommon and peculiar situation, with respect to the spectator 

 and the sun. It may be observed, that but one of these three 

 rainbows was real, the rest being only reflections thereof. It 

 may also be observed, that whenever the spectator stands be- 

 tween the sun and a cloud of falling rain, a rainbow is seen, 

 which is nothing more than the reflection of the different colour- 

 ed rays of light from the bosom of the cloud. If, for instance, 

 we take a glass globe, filled with water, and hang it up before 

 us opposite the sun, in many situations it will appear transparent ; 

 but if it is raised higher, or sideways, to an angle of forty-five 

 degrees, it will at first appear red ; altered a very little higher, 

 yellow ; then green, then blue, then violet colour : in short, it 

 will assume successively all the colours of the rainbow ; but, if 

 raised higher still, it will become transparent again. A falling 

 shower may be considered as an infinite number of these little 

 transparent globes, assuming different colours, by being place d 

 at their proper heights. The rest of the shower will appear 

 transparent, and no part of it will seem coloured j but such as 

 are at angles of forty-five degrees from the eye, forty-five de- 

 grees upward, forty-five degrees on each side, and forty-five de- 

 grees downward, did not the plane of the earth prevent us. We 

 therefore see only an arch of the rainbow, the lower part being 

 cut off from our sight by the earth's interposition. However, 

 upon the tops of very high moiuitains, circular rainbows are seen, 

 because we can see to an angle of forty-five degrees downward, 

 as well as upward, or sideways, and therefore we take in the 

 rainbow's complete circle. 



In those forlorn regions round the poles, the meteors, though 

 of another kind, are not less numerous and alarming When 

 the winter begins, and the cold prepares to set in, the Ffimr' m'sty 



