200 PHYSIOLOGICAL BOTANY. PART II. 



deepest shade of grey from (6) to (c), then all the shades 

 shades of grey may be 

 added, increasing in 

 their intensity from 

 (n) to (6), and all 

 those of blue from (6) 

 to (c), and the re-' 

 quired results will be 



obtained for this single basial colour. The impure co- 

 lours thus formed will also be of their deepest shades. 



As we have assumed twelve pure colours out of the 

 innumerable sets which might be formed so we may 

 assume two impure colours corresponding to each of 

 our basial colours, as sufficient for representing the 

 tertiary compounds. Those may be selected which lie 

 exactly intermediate between () and (f>), and (6) and 

 (c) (fig. 155.). The former will evidently contain a 

 double proportion of a pure colour mixed with one of 

 grey ; and the latter a double proportion of grey 

 mixed with one of pure colour. Thus we shall have 

 one set of "impure" and another of "very impure" 

 colours. 



(186.) Chromatometer. It will be seen that we 

 have considered the construction of twelve " pure" 

 colours, twelve "impure" colours, and twelve "very im- 

 pure" colours to be sufficient for our scheme. But we 

 may further adopt three separate shades of each of 

 these thirty-six colours, to which we may also refer the 

 shades of all natural colours ; and this gives us 108 

 different shades. If to these we add three correspond- 

 ing shades of grey we shall have in all 111 to complete 



he scheme. These may be arranged in a diagram 

 termed a "Chromatometer," which will serve for purposes 



