PHYSICAL AND LITERARY. 79 



of air, becomes reddifli j as we have faid 

 above. 



To underftand diftindly why the fun'^ 

 rays, by paffing thro' a greater and greater 

 quantity of air, change by degrees from 

 white to yellow, thence to orange, and laftly 

 to red, we have only to apply to the atmo- 

 fphere, what Sir Jfaac fays (Book I. of his 

 Optics, part 2. prop. 10.) concerning the 

 colour of tranfparent liquors in general. 



Is it not the fame coloured light of the 

 rifmg and fetting fun which tinftures the 

 clouds, that, being thrown by the refraftioix 

 of the atmofphere into the earth's fhadow^ 

 gives the moon fometimes, in total eclipfes» 

 the obfcure reddifh colour of brick ? A^ 

 the rays which pafs thro' the greateft tra6l oJT 

 air, become reddifh ; thofe which pafs thro* 

 the leafl, yellowifh ; and the intermediate 

 ones, orange : the red muft converge fafteft 

 into the fhadow ; after them, the orange j 

 and laftly, the yellow : fo, that the whole 

 fpace of the earth's fhadow, from the point 

 of the cone to about femidiameters from 

 the earth, being filled with a faint light, 

 whofe colours verge always more to red 

 in approaching the earth ; the colour c^f the 



moon. 



