CHAPTER III 
THE BLUE SKY 
THE two great expanses, the blue ocean at 
our feet and the blue sky over our heads, are 
both impressive in vastness—the ocean more 
than the sky, possibly because we are familiar 
with its extent and have felt its power. We 
know, in a vague way, that the sky is even 
vaster than the sea, that it is the open field 
leading into interminable space ; but its very 
obvious coloring, its apparent arch on all sides 
springing upward and inward from the horizon, 
its fixity, give us something of a false impres- 
sion. We are inclined to regard it as a great 
blue dome or roof, a something tangible that 
is supported by the horizon-rim, a concave sur- 
face looked a¢ instead of a vast transparency 
looked through. 
And there is some excuse for our regarding 
the blue sky as an actual surface. It is the 
outer envelope of the globe, and is made upof the 
blue rays of the sun reflected from atmospheric 
47 
Impres- 
sions of the 
sky. 
