INORGANIC EVOLUTION. 



[CHAP. 



are arranged in the order of Mendeleeff 's groups, and the irregularities 

 touching the total number of series, of principal series, the simple or 

 compound nature of the lines of each series, and percentage of lines 

 picked up by the various series, can all be gathered from an inspection 

 of the table. 



With regard to the stated absence of " principal series " in the case 

 of zinc, cadmium, and mercury, it may be pointed out that in each 

 case a very strong broad reversed line in the ultra-violet may repre- 

 sent the principal series; and in the case of copper, silver, and gold, 

 each of these elements contains in the ultra-violet a very strong pair of 

 lines which may represent the principal series. 



