Manchester Memoirs, Vol. li. (1906), No. %. 3 



each of these series, and have put forward suggestions as 

 to its possible cause in my first paper on the " Origin of 

 Elementary Substances," published in the Proceedings of 

 the Society, 1878, and Memoirs, 1887. 



In my later tables it will be seen that the alkaline- 

 earth metals are of small specific gravity which increases 

 with their atomic weight. Thus we have calcium, sp. g. 

 1-58; strontium, 2-54; barium, 375; radium, 4-8 approxi- 

 mate. Now, as the atomic weights of both series of 

 elements increase by definite increments of 23 and 24 

 respectively, it follows by just analogy that if the series 

 H2n were continued, the next member after lead would 

 have an atomic weight of 232 (208 + 24) or seven units 

 higher than Mme. Curie's determination for radium, with 

 an approximate specific gravity of 7. Another increment 

 of 24 would give 256, or two units less than the atomic 

 weight assigned by Runge and Precht for radium. But 

 this number would transfer the new element from the 

 series of alkaline-earth metals to the alternate series of 

 heavy metals containing lead and zinc. Moreover, in 

 none of the series of elements is there any with atomic 

 weights so high as 225 and 256 correlated with specific 

 gravity so low as 5 or 7. The determinations of Mme. 

 Curie, and Runge and Precht, therefore, afford no reason 

 for changing the position of radium in my table of 

 elements as the next higher member of the alkaline- 

 earth metals to barium, with an atomic weight of 184, 

 and a proximate specific gravity of 5. 



I have shown in former papers that helium is the 

 typical element of the series H2n, with an atomic weight 

 of 2 (He = 2), a value now adopted by French chemists 

 in the Table of atomic weights published in the Annuaire 

 du Bureau des Longitudes. This value agrees with those 

 of the other elementary gases (H, O, N, Ci), the atomic 



