8 Mr. Henry Wilde on Helium and 



sions of Lockyer and of Runge and Paschen be accepted, 

 i.e., that the new gas is a mixture, the density of helium 

 proper will be further increased. 



The low specific gravity of the cleveite gas, and its 

 occlusive affinity for the platinum electrodes of the 

 vacuum-tubes during the transmission of the electric 

 discharge, as first noticed by Lockyer, indicate that 

 helium proper is the typical element H3 at the head of 

 the uneven series H37Z, homologous in position and 

 analogous in properties with hydrogen, and that the 

 lighter constituent of reputed helium is the typical element 

 H2 at the head of the positive even series H2«. Further 

 research, however, is necessary before the characteristic 

 lines belonging to each of the constituents of reputed 

 helium can be determined with certainty, and the 

 complete separation of the other new gases obtained 

 from minerals by the distillation method is the problem 

 which awaits solution. 



* I have shown in former papers that the characteristic 

 spectral lines of the alkaline metals in the series H11, and 

 their homologues of position in the series H311 containing 

 thallium and its analogues, indium and gallium, advance 

 towards the more refrangible end of the spectrum in the 

 inverse order of their atomic weights. t The same relation 

 is also observable in the spectra of the alkaline-earth 

 metals, and in other well-defined series of elements. 

 M. Lecoq de Boisbaudran had previously formulated the 

 same relation towards the less refrangible end of the 

 spectrum, in the direct order of the atomic weights. X 



* Note read before the Society, October 15, 1895. 



t Memoirs Manchester Lit. and Phil. Soc, 1878, 1887, 1895. Proc. Eoy. 

 Soc, 1893. 



\Comptes Rendus, Vol. LXIX., 1869. 



