"And if you look intensely 
at the pure blue of a serene sky, 
you will see that there is a variety and fullness 
in its very repose. 
It is not flat dead color, 
but a deep, quivering, transparent body of penetrable air, 
in which you trace or imagine 
short, falling spots of deceiving light,
 and dim shades,
 faint, veiled vestiges of dark vapor; 
and it is this trembling transparency 
which our great modern master 
has especially aimed at and given." 
~ John Ruskin