io Helium in the Classification of Elementary Substances. 



or even series of elements have to each other than to the 

 immediately adjoining series. Hence the spectra of Ga, 

 In, Tl, in the third series, have a greater resemblance to 

 the spectra of their homologues of position, K, Rb, Cs, in 

 the first series, than they have to their homologues Ca, Sr, 

 Ba, in the second (even) series. The chemical and other 

 properties of hydrogen and the two constituents of 

 reputed helium (H, H2, H3) may, therefore, be expected 

 to stand in the same order to each other as their homo- 

 logues of position in the first, second, and third vertical 

 series of elements, Hn, ~H.2n, H3», as shown in my table. 



Professors Runge and Paschen, in their endeavour to 

 bring the two new gases into a classification in accordance 

 with the requirements of Mendeleeff's so-called periodic 

 law, have placed them in the first series between hydrogen 

 and lithium, notwithstanding that they, at the same time, 

 show that the spectra of these gases shift in the opposite 

 direction to the spectra of the alkalies Li, Na, K, Rb, Cs. 



The German physicists can hardly have realised the 

 consequences to Mendeleeff's system of placing the two 

 gases between hydrogen and lithium. In the paper which 

 I read before the Society in December last, I gave a 

 demonstration of the confusion that would be brought into 

 the so-called periodic system by the discovery of a new 

 element x in the particular series where these physicists 

 propose to place the new gases.* There is absolutely no 

 place in Mendeleeff's system for elements with atomic 

 weights between lithium and hydrogen, as the Russian 

 chemist never contemplated the existence of elements with 

 properties and cosmical relations such as the new gases 

 have been found to possess. 



'Memoirs Manchester Lit. and Phil. Soc., Vol. IX., p. 77. 



