XXIII.] FROM A CHEMICAL STANDPOINT. 183 



the spectra full of lines which we see at the temperature of the arc, 

 and metals of relatively high atomic weight and melting point are 

 involved ; the exact sequences are naturally more difficult to follow, 

 and therefore the method of evolution may escape us. 



Kayser and Runge have shown that the melting point has a pro- 

 found influence on the " series " conditions. Those with the highest 

 melting points, such as barium and gold, present us with no series. 

 There is generally such a flood of lines that it has been so far impos- 

 sible to disentangle them ; we have the " structure spectrum " of 

 hydrogen repeated in these metals at arc temperatures in the so-called 

 " arc spectrum." 



I have already said that I think most chemists would consider 

 that the formation of larger masses by polymerisation is more probable* 

 than by the coming together of dissimilar atoms ; but if we consider 

 chemical compounds, certainly the analogy is all in favour of the 

 latter view if the principle of continuity be taken into account, for we 1 

 are ignorant of the point at which one evolutionary process resigns in 

 favour of another. The present separation of compound from simple 

 bodies is, indeed, simply a measure of our ignorance arising from the 

 feebleness of our laboratory resources in relation to the temperature 

 required to produce more and more simplifications. 



I discussed the question in my Chemistry of the Sun in 1887, 

 and showed that the analogy of the completely studied hydrocarbon 

 series beginning with CH 2 suggested 1 a hypothetical elemental 

 sequence. 



a b, separate. 



a + b, combined. 



a + (b + b), written by chemists ab. 2 . 



+(* 2 )c* 2 ) C 



and so on. 



In the concrete hydrocarbon series we have continuous additions 

 of CH 2 to CH 4 until we reach a molecule defined by C^H^, and as 

 the building up of this molecule can be traced without difficulty, so 

 we can imagine it simplified by successive shedding 's of its constituent 

 CH 2 ; we pass from a simplification which we can bring about by 

 simple halving to one which provides us with relatively large and 

 small masses. 



