7« ESSAYS AND OBSERVATIONS 

 fame colours much more rich and copious 

 in the clouds, is their femir-tranfparency joined 

 with the obliquity of their fituation. 



Does it not greatly confirm this explica- 

 tion, that thefe coloured clouds immediately 

 refume that dark leaden hue which they re- 

 ceive from the (ky as foon as the fun's dire<n: 

 rays ceafe to ftrike upon them ? For, if 

 their gaudy colours arofe, like thofe of the 

 foap-bubble, from the particular fize of their 

 parts, they would preferve nearly the fame 

 colours, tho' much fainter, when illumi- 

 nated cnly by the atmofphere. About the 

 time of fun-fet or a little after, the lower part 

 of the iky, to fome diflance on each fide front 

 the place of his fetting, feems to incline to 

 a faint fea-green, by the mixture of his 

 tranfmitted beams, which are then yellowilh, 

 with the ethereal blue : at greater diftances, 

 this faint green gradually changes into a red- 

 difh brown ; becaufe the fun's rays, by 

 pafling thro' more air, begin to incline to 

 orange : and, on the oppofite lide of the 

 hemifphere, the colour of the horizontal 

 fky inclines fenfibly to purple j becaufe his 

 tranfmitted light which mixes with the 

 a^ure, by paffing thro' a ftill greater length 



of 



