Permanent Colours of Opake Bodies, 235 



which are oppofed to the rays tranfmitted 

 through the aimofphere, refled their light, and 

 thence affiime their colours. 



Sir Ifaac Newton attributed the various colours 

 of the clouds, to the different magnitudes of the 

 particles, whereby he conceived that they were 

 qualified to refled: the differently refrangible 

 rays. M. Melvill has more accurately remark- 

 ed, that the colours of the clouds, at fun-rifins 

 and fetting, do not depend on the fizes of their 

 component particles, but arife merely from the 

 colours of the rays tranfmitted through the tradb 

 of air which is contiguous to the horizon, and 

 that they indifcriminately refle6t the rays which 

 are incident upon them. 



This obfervation perfedlly agrees with the 

 phenomena. But the author of this remark 

 does not feem to have formed any clear or 

 precife conception of the conftitution of the 

 atmofphere, and its aflion on the rays of light. 

 He fuppofed, that the atmofphere is fimilar 

 to Tranfparent Coloured Liquors. * But, it 



• Phyfical EfTays: Edinburgh. 1756. vol. 11. p. 79. 

 ♦' To underftand why the fun's rays, by pafling through 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 atmofphere, what Sir 

 " Ifaac Newton fays (Book I. of his Optics, Part. II. Prop. 

 ♦' X.) concerning the colour of tranfparent liquors in 

 •' general." 



appears 



