THEORY OF THE SYSTEM. . 219- 



of the series of individuals, every property being taken 

 into consideration, becomes 



II. ... P. b. (X + n) ; Q. c. (X + n); R. d. (X + n) ; 

 S. e. (X + n) ; . . . 



The individual connecting the two series, or that which 

 at the same time is a member of the series I. and a mem- 

 ber of the series II. ; must necessarily possess the form 

 (X + n) and the colour a, the rest of its properties coincid- 

 ing exactly with those of the two series. If, for the indi- 

 vidual above mentioned, we designate that aggregate by N, 

 the individual itself will be : 



N. a. (X + n). 



For under these circumstances its properties, excepting 

 the form, agree entirely with those of series I. ; and this 

 form is a member of the series X, X 4- 1, &c. ; whilst in 

 the same manner, excepting its colour, it agrees exactly 

 with series II. ; its colour being a member of the series 

 b, c, . * . 



We are led by experience to assume such relations as 

 those mentioned above. Suppose, for instance, A, B, C, ... 

 P, Q, R, ... in the above signification of the letters, to be 

 varieties of octahedral Fluor-haloide. Let the members 

 of the series of forms in I. be * the dodecahedron (D), the 

 octahedron (O), a digrammic tetragonal-icositetrahedron 

 (I), a tetraeonta-octahedron (T) ... and the colour grass- 

 green (gg) ; the series of individuals will be 



A.gg.O; B.gg.D; C.gg.I; D.gg.T . . . 



In the series II. the series of colours may be apple- 

 green (ag), mountain-green (mg), verdigris-green (vg), sky- 

 blue (sb)... and their form the hexahedron (H) ; the series 

 of individuals therefore 



. . . P. ag. H ; Q. mg. H ; R. vg. H ; S. sb. H . . . 



The above mentioned forms and colours have not only 



* We may choose whatever forms of the series of crys- 

 tallisation, and whatever varieties of the series of colours 

 of octahedral Fluor-haloide ; we shall always derive the 

 same results. 



