98 INORGANIC EVOLUTION. [CHAP, 



there are no series at all. In the case of lithium, sodium, potassium, 

 &c., all the lines are picked up ; in the case of copper, silver, and gold, 

 the series pick up only a very small proportion. There seems, there- 

 fore, to be a progression of complexity with the increasing melting 

 point with regard to all the metallic substances which have so far been 

 examined. 



In the case of barium with a high melting point, we get no lines at 

 all represented in "series" : contrasted with 100 per cent, in the case 

 of lithium. But then again, when we come to mercury, which is also 

 of low melting point, instead of getting 100 per cent, we only get 

 about 25 per cent, of the lines represented. The metals then vary as 

 do the gases. 



General Conclusions. 



The evidence then seems to indicate that the chemical units in the 

 case of the elements studied by the movements written out by these 

 series must possess different degrees of complexity. A little time ago 

 it was imagined that hydrogen was rendered visible to us by such 

 simple vibrations that only one series of lines could be produced. If 

 that is so, then it looks very much as if whenever we see three series 

 of lines at least three molecules or atoms, three different things, are 

 in all probability at work in producing them. When we get six 

 series, that points to a still greater complexity, and when, as in the 

 case of oxygen, we get six series not accounting for half the lines, then 

 we should be quite justified, I think, in supposing that oxygen was one 

 of the most complex things that we were brought face to face with in 

 our studies of " series " in cases where they are observable. When we 

 come to metals where there are no series at all, what do we find 1 We 

 are dealing with substances with high melting points that is to say, 

 we cannot bring them down easily to those mobile states represented 

 by the free paths and collision conditions of a permanent gas ; and it 

 is quite easy to suppose, on that account alone, that we do not see the 

 vibrations of any of the more simple forms. 



Hence, then, I submit that the evidence presented as to the com- 

 plex origin of line spectra by the studies of " series " is as clear as that 

 obtained from high temperature work in the laboratory and a discus- 

 sion of stellar spectra in relation to that work. 



I have already referred to the case of hydrogen. 



Professors Pickering and Kayser both concede that the new series, 

 is due most probably to a high temperature, and Kayser expressly 

 states, " that this series has never been observed before, can perhaps be 

 explained by insufficient temperature in our Geissler tubes and most o 

 the stars." 



