SCIENCE 



[N. S. Vol. XLIX. No. 1253 



the proportion by weight in which it combines 

 with some other element, taken as a standard. 

 There is no need, before this distinguished 

 audience, of emphasizing the importance of 

 the familiar table of atomic weights ; but a few 

 parenthetical words about their character is 

 perhaps not out of place. As has been more 

 than once said, the atomic weights of the 

 relatively permanent elements, which consti- 

 tute almost all of the crust of the earth, seem 

 to be concerned with the ultimate natm:e of 

 things, and must have been fixed at the very 

 beginning of the universe, if indeed the uni- 

 verse ever had any beginning. They are 

 silent, apparently unchanging witnesses of the 

 transition from the imagined chaos of old 

 philosophy to the existing cosmos. The crystal 

 of quartz in a newly hewn piece of granite 

 seems, and probably is, as compact and perfect 

 as it was just after it was formed, eons ago. 

 We can not imagine that any of its properties 

 have essentially changed during its protracted 

 imprisonment; and, so far as we can guess, 

 the silicon and oxygen of which it was made 

 may have existed for previous eons, first as 

 gas, and then as liquid. The relative weights 

 in which these two elements combine must 

 date at least from the inconceivably distant 

 time when the earth " was without form and 

 void." 



Although, apparently, these numbers were 

 thus determined at the birth of our universe, 

 they are, philosophically speaking, in a differ- 

 ent class from the purely mathematical con- 

 stants such as the relation of circumference 

 to the diameter of a circle. 3.14159 ... is a 

 geometrical magnitude entirely independent 

 of any kind of material, and it therefore be- 

 longs in the more general class of numbers, 

 together with simple numerical relations, log- 

 arithmic and trigonometric quantities, and 

 other mathematical functions. On the other 

 hand, the atomic weights of the primeval ele- 

 ments, although less general than these, are 

 rauch more general and fundamental than the 

 constants of astronomy, such as the so-called 

 constant of gravity, the length of the day and 

 year, the proper motion of the sun, and all the 

 other incommensurable magnitudes which have 



been more or less accidentally ordained in the 

 cosmic system. The physicoehemical con- 

 stants, such as the atomic weights, lie in a 

 group between the mathematical constants 

 and the astronomical " constants/' and their 

 values have a significance only less important 

 than the former. 



In the lead from loranium, we have a com- 

 paratively youthful elementary substance, 

 which seems to have been formed since the 

 rocks in which it occurs had crystallized. Is 

 the atomic weight of this youthful lead 

 identical with that of the far more ancient 

 common lead, which seems to be more nearly 

 contemporary as to its origin with the silicon 

 and oxygen of quartz? 



The idea that different specimens of a given 

 element might have different atomic weights 

 is by no means new — it far antedates the dis- 

 covery of radioactivity. 



Ever since the discovery of the definite com- 

 bining proportions of the elements and the 

 ascription of these proportions to the relative 

 weights of the atoms, the complete constancy 

 of the atomic weights has occasionally bepn 

 questioned. More than once in the past in- 

 vestigators have found apparent differences in 

 the weights of atoms of a single kind, but 

 xmtil very recently all these irregularities have 

 been proved to be due to inaccurate experi- 

 mentation. N'evertheless, even thirty years 

 ago the question seemed to me not definitively 

 answered, and careful experiments were made 

 with copper, silver and sodium, obtained from 

 widely different sources, in the hope of find- 

 ing differences in the atomic weights, accord- 

 ing to the source of the material. No such 

 differences whatever were found. More re- 

 cently Professor Baxter, of Harvard, com- 

 pared the atomic weights of iron and nickel in 

 meteorites (from an unknown, perhaps in- 

 conceivably distant source) and the same 

 terrestrial metals. In these cases also the 

 results were negative. Thus copper, silver, 

 sodium, iron and nickel all appeared to be 

 perfectly definite in nature, and their atoms, 

 each after its own kind, all alike. 



The general question remained, neverthe- 

 less, one of profound interest to the theoretical 



