THE 

 LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FIFTH SERIES.] 



DECEMBER 1879. 



LI. A new Explanation of the Colour of the Sky. 

 By E. L. Nichols, Ph.D n Gottingen*. 



IN seeking an explanation of the colour of the sky, there is 

 little use in looking back beyond Newton. Other philo- 

 sophers f had discussed the question ; but their reasoning was 

 not such as, in the present state of science, demands our 

 earnest attention. Newton's opinion stands to this day as 

 near the truth perhaps as any later hypothesis J: — 



" The blue of the first order, though very faint and little, 

 may possibly be the colour of some substances ; and particu- 

 larly the azure colour of the skies seems to be of this order ; 

 for all vapours when they begin to condense and coalesce in 

 small parcels, become first of that bigness whereby such an 

 azure must be reflected, before they can form clouds of other 



* Communicated by the Author. 



t Forbes, " On the Colours of the Atmosphere," ' Edinburgh Trans.' 

 1840, reviews in an interesting- manner the older authorities on this sub- 

 ject. Of these, Leonardo da Vinci, Traite de la Peinture, considered the 

 blueness of the sky as simply the effect upon the eye of looking into the 

 infinity of space. Mariotte, GEuvres, i. 229, insisted upon an actual blue 

 colour of the air ; and Euler (1762) said, " It is more probable that all the 

 particles of the air should have a faintly bluish cast, but so very faint as 

 to be imperceptible, until presented in a prodigious mass." Muncke, on 

 the contrary, declared the colour of the heavens to be an optical illusion, 

 something purely subjective (see Gehler's Worterbuch, article Atmo- 

 sphare). Even Sir David Brewster seems to have had doubts as to the 

 reality of the sky's blueness. 



% Newton, ' Optics,' Book II. 



Phil. Mag. S. 5. Vol. 8. No. 51. Dec. 1879. 2 G 



