SKY

, the blue expanse of the air or atmosphere.

The azure colour of the sky is attributed, by Newton, to vapours beginning to condense, having attained consistence enough to reflect the most reflexible rays, viz, the violet ones; but not enough to reflect any of the less reflexible ones.

De la Hire attributes it to our viewing a black object, viz the dark space beyond the regions of the atmosphere, through a white or lucid one, viz the air illuminated by the sun; a mixture of black and white always appearing blue. But this hypothesis is not originally his; being as old as Leonardo da Vinci.