xxvii.] NEW LINES. 391 



strongly reversed, the other two lines remaining bright, they 

 certainly might have put this forward as an objection to my 

 view, and I confess it would be very difficult to reply to it. 



Messrs. Liveing and Dewar also refer to new absorption lines 

 which are produced when magnesium and sodium vapours, or 

 magnesium and potassium vapours, are mixed. 



Such a result is entirely in harmony with my hypothesis, and 

 seems to me to indicate that some of the finer molecules of 

 these substances can combine together at high temperatures 

 and produce new bodies, although it may be impossible to 

 obtain them in the cold ; and yet they remark : l 



" The observations on the spectrum of magnesium have a special 

 interest, because from the close analogy of magnesium to zinc and 

 cadmium, it is referred that the molecules of magnesium vapour are 

 chemical atoms of that substance, that is to say, they pass apparently 

 undivided through all the chemical changes to which magnesium 

 may be subjected ; and it seems reasonable to suppose, that any 

 subdivision of the chemical atoms could not fail in this case to be 

 attended with a change of chemical qualities, which in the presence 

 of other elements would, give rise to new compounds. No such new 

 compounds have in fact been detected? 



I gather elsewhere 3 that Messrs. Liveing and Dewar have 

 obtained no " independent " evidence of the existence of these 

 compounds. One of the difficulties of the problem of course is, 

 that new substances, even if we acknowledge them to exist at the 

 temperature of the arc, cannot be collected and put into bottles. 

 But this must not be used as a final argument, for if it be, 

 what, as has been well said, would become of the chemical atom 

 and the chemical molecule ? Messrs. Liveing and Dewar state 

 moreover, that although they have not obtained the emission 

 spectra in the case of these two substances, supposing them to 



1 Proc. Roy. Soc. vol. xxxiii. p. 428. 



2 The italics are mine. J. N. L. 



3 Proc. Roy. Soc. vol. xxx. p. 97. 



