in Thoreau’s Journal:

The drifting, white downy clouds are to the landsman what sails on the seas are to him who dwells by the shore, objects of a large, diffusive interest….They are the flitting sails in the ocean whose bounds no man has visited. They are like all great themes, always at hand to be considered, or they float over us unregarded. Far away they float in the serene sky, the most inoffensive of objects, or near and low they smite us with the lightnings and deafen us with their thunder….

What could a man learn by watching the clouds? These objects which go over our head unobserved are vast and indefinite….They are among the most glorious objects in Nature. A sky without clouds is a meadow without flowers, a sea with sails.