Page:Scientific Memoirs, Vol. 1 (1837).djvu/112

100 but very imperfectly that of the colours in the prismatic spectrum.

My scale is developed in such a manner that no illusion can take place. The interval comprised in the second ring is entirely free from green; neither is it to be found in the first order. Hence it is inferred, that among the thin layers of the two first orders there is none capable of reflecting any portion of green. The result is curious, and we have remarked it in the hope that, under different circumstances, it may be turned to account.

In speaking of the tints of the first ring we have stated that they are further removed than the others from the nature of the prismatic colours. The tints which, on the contrary, approach it most nearly are those of the second ring: yet even these are too distinct from it to be confounded with the simple colours of the prism. We have the sky, their type in nature, constantly before our eyes; for who is there that knows not the dawn, "with rosy forehead and golden feet"? Beginning with No. 12 of the scale, let us run our eye over it as far as No. 28, and we shall find the tints of the sky disposed there in the order in, which they present themselves in the magnificent spectacle of the dawning day. This succession, as we have already observed, is the most beautiful of all: Newton's second ring gives no idea of it, because its colours are not, and cannot be, sufficiently developed to produce the effect. Painters, if I mistake not, will do well to avail themselves of this part of the scale: they will find in it a faithful copy of the beautiful tints of the morning, and endeavour to transfer them to their compositions. Natural philosophers will not fail to remark, that among the various tints of the sky there is no trace of green. This would heretofore have been found a perplexing circumstance, but may now be satisfactorily explained, merely by reflecting that the tints of the sky belong to the second order, in which also there is no tinge of green. From the blue to the yellow the transition is through a very faint gradation of azure-yellow, and this is observed to be exactly the case in nature.

The tints produced by vapours and clouds belong to the second order. They contain in general more fire than the natural tints of the sky, but this quality is nothing in comparison with the purity, vividness and variety displayed in the tints of the second order. The appearance of the sun is never so magnificent as when the air is perfectly pure. Toward evening the lower regions of the atmosphere are always more or less