On the Colour of the Atmosphere and Deep Water, 349 



same thing is observed in some other siliceous stones, although 

 it is still more remarkable in opaline glasses ; a weak solution 

 of soap produces the same appearance, and it is more striking 

 in the jelly of the fish of Astracan, while an infusion of the 

 bark of the chestnut is perfectly opaline. Newton mentions a 

 kiad of wood which he calls nephritic, an infusion of which is 

 opaline. Lastly, the amber found in the Sicilian sea, at the mouth 

 of the Giarreta (the ancient Simcethus) is greatly prized on ac- 

 count of the opaline property, which it possesses in the highest 

 perfection *. 



A blue reflection is observed in certain bodies which are white 

 and opaque, when they are reduced to a sufficient thinness to 

 transmit the light ^ a familiar example of this occurs in the 

 skin that covers the veins, which is blue, although neither the 

 skin nor the blood are of that colour. 



Finally, the mixture of white with black, and with transpa- 

 rent colouring substances in painting, present numerous exam- 

 ples of the pi;o4uction of opaline blue, which shall be afterwards 

 described, .^r .>.i, .djwoi^ 



This blue colour is the only one which admits of being ex- 

 plained on the theory of thin plates, supposing that the particles 

 of opaline bodies are of the size requisite for reflecting blue. 

 This explanation becomes probable when it is considered that, 

 the colour transmitted by these bodies is the yellow comple- 

 mentary of the reflected blue ; but the object of this essay is 

 only to point out the phenomenon in the substances which 

 produce it, and to describe the effects, without admitting the 

 truth of this theory, to which there are considerable objections. 



The examination of opaline substances, and their action on 

 the light that is reflected and transmitted, will shew clearly the 

 analogy which exists between their colours and those observed 

 in the air and in water^ and will prove that the same cause pro- 

 duces the phenomenon in all bodies where it occurs. , mmr, -ni i 



In preparing opaline glass, the powder of calcined bones is •' 



been attributed to natural iissures. This was the opinion of the celebrated 

 Hatty. ,. ,, . <Scv!;tM»:tnot. ^1' irnorvnUf i^U»;^ni^«m> 



• One oi^ the tributaries of the Giarreta flows at the fh«t of Etna; and - 

 this modification of amber, which does not occur elsewhere, is no doubt owing 

 to the influence of the volcano. It is likewise found in this place of a ruby 

 red colour, as well as green and black. 



