Manchester Memoirs, Vol. xlviii. (1903), No. 1. 5 



atomic weights than those shown in each series of the 

 Table. 



The electro-positive series H2n has long been remark- 

 able for the property of phosphorescence which some of 

 its lower members possess above those of the other series 

 of elements. Thus, calcium sulphide (Canton's phosphorus 

 or Balmain's paint), and barium sulphide (Bolognian 

 phosphorus) become luminous when exposed to the action 

 of solar or electric light, and retain their luminescence for 

 a considerable time after the source of light has been 

 removed. 



Radium has been shown by its discoverers, M. and 

 Mme. Curie, to be the next higher member of the calcium, 

 strontium and barium series (H2n) of alkaline earth 

 metals, and that its halogen compounds are permanently 

 self-luminous. 



I have already indicated the remarkable interruption 

 in the regularity of the multiple series H2n through the 

 absence of elements with atomic weights 160 and 184 

 respectively, the numerical order being resumed with the 

 atomic weight of lead 208. These gaps in the series 

 are the more striking from their being exactly paralleled 

 by the absence of two members in homologous positions 

 in the series Hn, with atomic weights 154 and 177, the 

 multiple order being resumed by the atomic weight of 

 mercury 200. These lacunse obviously indicate the 

 existence of undiscovered elements, or of elements 

 transmuted or in the process of transmutation. 



As there is only one place vacant higher in the series 

 H2n for an analogue of calcium, strontium and barium, 

 alternating with zinc, cadmium and lead, radium is 

 identified as the tenth elementary condensation of H2, 

 with an atomic weight of 184, and a specific gravity of 48, 

 as shown in my Table. 



