THE COLOR OF THE SKY. 61 



heaven, ' from the zenith to the horizon, becomes one 

 molten, mantling sea of color and fire ; every black 

 bar turns into massy gold, every ripple and wave into 

 unsullied shadowless crimson, and purple, and scarlet, 

 and colors for which there are no words in language, 

 and no ideas in the mind things which can only be 

 conceived while they are visible ; the intense hollow 

 blue of the upper sky melting through it all, showing 

 here deep, and pure, and lightness ; there, modulated 

 by the filmy, formless body of the transparent vapour, 

 till it is lost imperceptibly in its crimson and gold.' 



But what is the explanation of these gorgeous 

 colors ? why is the sky blue ? and why are the sunrise 

 and sunset crimson and gold ? It may be said that the 

 air is blue, but if so how can the clouds assume their 

 varied tints ? Briicke showed that very minute particles 

 suspended in water are blue by reflected light. Tyndall 

 has taught us that the blue of the sky is due to the re- 

 flection of the blue rays by the minute particles floating 

 in the atmosphere. Now if from the white light of the 

 sun the blue rays are thus selected, those which are 

 transmitted will be yellow, orange, and red. Where 

 the distance is short the transmitted light will appear 

 yellowish. But as the sun sinks towards the horizon 

 the atmospheric distance increases, and consequently 

 the number of the scattering particles. They weaken 

 in succession the violet, the indigo, the blue, and even 

 disturb the proportions of green. The transmitted 

 light under such circumstances must pass from yellow 

 through orange to red, and thus, while we at noon are 

 admiring the deep blue of the sky, the same rays, robbed 

 of their blue, are elsewhere lighting up the evening sky 

 with all the glories of sunset. 



