I add here Chapman's version of the other passage, which is extremely beautiful and close to the text, while Pope's is hopelessly erroneous.
"Their ground they still made good, And in their silence and set powers, like fair still clouds they stood, With which Jove crowns the tops of hills in any quiet day When Boreas, and the ruder winds that use to drive away Air's _dusky vapors_, being _loose_, in many a whistling gale, Are pleasingly bound up and calm, and not a breath exhale."]
[Footnote 14: 'Reflected.'--The reader must be warned in this place of the difference implied by my use of the word 'cast' in page 11, and 'reflected' here: that is to say, between light or color which an object possesses, whatever the angle it is seen at, and the light which it reverberates at one angle only. The Alps, under the rose[A] of sunset, are exactly of the same color whether you see them from Berne or Schaffhausen. But the gilding to our eyes of a burnished cloud depends, I believe, at least for a measure of its luster, upon the angle at which the rays incident upon it are reflected to the eye, just as much as the glittering of the sea beneath it--or the sparkling of the windows of the houses on the shore.
Previously, at page 10, in calling the molecules of transparent atmospheric 'absolutely' unreflective of light, I mean, in like manner, unreflective from their _surfaces_. Their blue color seen against a dark ground is indeed a kind of reflection, but one of which I do not understand the nature. It is seen most simply in wood smoke, blue against trees, brown against clear light; but in both cases the color is communicated to (or left in) the _transmitted_ rays.
So also the green of the sky (p. 13) is said to be given by transmitted light, yellow rays passing through blue air: much yet remains to be known respecting translucent colors of this kind; only let them always be clearly distinguished in our minds from the firmly possessed color of opaque substances, like grass or malachite.
[Footnote A: In speaking, at p. 11 of the first lecture, of the limits of depth in the rose-color cast on snow, I ought to have noted the greater strength of the tint possible under the light of the tropics. The following passage, in Mr. Cunningham's 'Natural History of the Strait of Magellan,' is to me of the greatest interest, because of the beautiful effect described as seen on the occasion of his visit to "the small town of Santa Rosa," (near Valparaiso.) "The day, though clear, had not been sunny, so that, although the snowy heights of the Andes had been distinctly visible throughout the greater part of our journey, they had not been illuminated by the rays of the sun. But now, as we turned the corner of a street, the chain of the Cordillera suddenly burst on our gaze in such a blaze of splendor that it almost seemed as if the windows of heaven had been opened for a moment, permitting a flood of _crimson_ light to stream forth upon the snow. The sight was so unexpected, and so transcendently magnificent, that a breathless silence fell upon us for a few moments, while even the driver stopped his horses. This deep red glow lasted for three or four minutes, and then rapidly faded into that lovely rosy hue so characteristic of snow at sunset among the Alps."]]