100 M. NOBILI ON COLOURS, AND ON A NEW CHROMATIC SCALE 



sembles but very imperfectly that of the colours in the prismatic spec- 

 trum *. 



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 tliin 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 co- 

 lours. 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. 1 2 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 dawn- 

 ing 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 ef- 

 fect. 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 va- 

 riety 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 



• Professor Atnici has. been so kind as, at my request, to employ all the means 

 at his command in a careful examination of Newton's rings. He has seen them 

 exactly as I have; for he has found neither blue in the first nor green in the 

 second ring. I value the testimony of my illustrious friend and colleague too 

 highly not to avail myself of it in this case. 



