292 TERMINOLOGY. . 202. 



. 202. SERIES OF COLOURS. 



The varieties of colours occurring in the indivi- 

 duals of one and the same species, form an unin- 

 terrupted series, which is called the Series of Co- 

 lours of that Species. 



If we consider the colours occurring in a species, which is 

 pretty complete in this respect, we find that they insen- 

 sibly pass into each other, or that every one of them is in- 

 termediate between two others. Thus they represent an 

 uninterrupted succession of the shades of colours, and this 

 it is what is meant by the series of colours. 



The occurrence of the series of colours is the most im- 

 portant fact in respect to the present subject for the use of 

 Natural History. In order to obtain these series, by ab- 

 stracting from the rest of the natural-historical properties 

 of the individuals in any complete species, it is necessary to 

 exclude all those colours, which are derived from a mixture 

 with heterogeneous minerals ; as, for instance, the lemon- 

 yellow, and the blood-red colours of prismatic Hal-baryte, 

 the existence of which is owing to an admixture of certain 

 species of the order Sulphur ; or the yellowish-brown and 

 reddish-brown colours of rhombohedral and uncleavable 

 Quartz, arising from oxides of iron, &c. 



The series of colours cannot be described ; they must 

 necessarily be studied from nature ; but the little trouble 

 which this requires will be amply rewarded. In the 

 species of the order Gem, the most striking examples 

 occur. Octahedral Diamond, rhombohedral Corundum, 

 prismatic Topaz, rhombohedral Emerald, dodecahedral 

 Garnet, and rhombohedral Tourmaline, may serve as ex- 

 amples for the illustration of these series. The series 

 of colours of octahedral Fluor-haloide is one of the most 

 common, and very easily completed, at least to a certain 

 extent. This series comprehends a great variety of co- 

 lours, and resembles, in some respect, the series of colours 

 of octahedral Diamond and of rhombohedral Fluor-haloide. 



