PRODUCED BY ELECTRO-CHEMICAL ACTION. 101 
charged with vapours, the air no longer retains its morning transpa- 
rency, and the setting of the sun is attended by a fiery tint which 
greatly mars the tranquil beauty of the spectacle. It is to those vapours 
that we are to attribute the inflamed appearance of the sky, because 
they possess the power of transmitting the tints of the first order, and 
these are of that fiery cast. Were it not for this circumstance the set- 
ting of the sun might justly vie with its rising. 
Philosophers had long since settled their opinions as to the co- 
lours of the sky. These they explained by assigning to the air the 
property of reflecting the higher colours of the spectrum (violet, indigo, 
&c.), and that of transmitting the lower, (red, orange, &e.). The ex- 
planation was correct so far as it went, but to make it complete the 
exact quality of the tints should be determined by indicating the order 
to which they belong. It was necessary also to ascertain how light is 
affected by the presence of vapours. The considerations which we have 
just stated will perhaps supply both these deficiencies. 
_ Third and Fourth Rings-——From No. 29 to 38, and from 39 to 44. 
These two rings comprise (if I may use the expression) the richest 
tints. The tints of the first ring are distinguished by their fiery and 
metallic appearance ; those of the second by their transparency and 
vividness ; those of the third and fourth by their intensity, and by the 
presence of green, which is wanting in the first and second orders. The 
first appearance of green is in the third order at No. 32: it appears 
again in the fourth order at No. 41. These two greens differ but little 
from one another, and are both beautiful in a very high degree: they 
have a strong resemblance to the green of the emerald. The tints of 
the third ring do not differ much from those of the fourth: their most 
marked difference consists in the diminution of transparency observable 
in passing from the third to the fourth order. 
‘The colours contained in these two series abound in the three king- 
doms of nature ; the vegetable kingdom however seems to present them 
in the greatest proportion. 
The predominant colours in these two parts of the scale are the red, 
the green, and the yellow-green. There is here, properly speaking, no 
species of blue, but its absence is counterbalanced by the presence of 
the green, which is not to be found in the first two rings. It would 
seem as if the blue belonged peculiarly to the spacious vault of heaven, 
and the green to the surface of the earth. They are two dominant 
colours in nature, but their domains are separated, and the separation 
seems to me not to be accidental. It was necessary, I suppose, that the 
atmosphere should be composed of the most subtile particles, in order 
that they might remain suspended in space; the earth did not require 
to be of so delicate a texture. Hence we have two very distinct orders 
