s().\tF. coxTEMPoR.ih'y .tni-.ixci-s- IX rnysfcs-ir 479 



and plusiral proptTtios in passing alonR the line. Indeed the jx-riddie- 

 it\- was s*) dear thai in thnv instances vvlieii the order of two ronsecii- 

 tive elenuMits was such as to ilaniage the [x-riodii- law', rhemists simply 

 re\ersetl the order-putting argon In-fore potassium, cobalt la-fore 

 nickel, telluriunt In-fore iodine, thus testifying to a faith that there 

 must be something go\erning the nature of the chemical elements 

 more fundamental than o>mbining weights. Furthermore, in several 

 instances where the periodic law implieil that there ought to be an 

 additional element iK-twecn two apparently consecutive ones, chemists 

 left a vacant space lietween the two for an element presumed to be 

 existent but unknown; and some of these elements were subsequently 

 disco\ered, thus justifying the faith in the most impressive way. But 

 of the nature of this fundamental something, there was no inkling. 



It had been suggested at one time that all atoms are built up f)f 

 hydrogen atoms. But the most accurate measurements placed it 

 beyond doubt that the chemical combining weights of the elements 

 are not, in every' case, integer multiples of the combining weight of 

 h\drogen, nor of any other common divisor large enough to have a 

 physical meaning. As it was universally assumed that the weight 

 of the ultimate particles of an element is etiual to its combining 

 weight multiplied by some universal factor, this fact seemed to dis- 

 pro\e the suggestion. Yet on the other hand the measurements 

 established a rule that the combining weight of many of the elements 

 — far too many to be explained as due merely to chance — are integer 

 multiples of a common unit which is r^o of the combining weight of 

 oxygen. This can be illustrated from any group of elements, for 

 example from the first ten of the periodic table: 



out of which group o( numlxjrs eight are integer multiples of the unit 

 1.00, within observational error; while four — the combining weights 

 of hydrogen, lithium, boron and neon — certainly are not. We are 

 confronted with a manifest rule restricted by undeniable exceptions — 

 the most stimulating situation which can arise in a science. 



Suddenly the exceptions to the rule were all explained away, and 

 the mystery vanished with a completeness which we hope that some 

 of the other mysteries of physics will some day emulate. The trouble 

 was simply that everyone has assumed, with an indifference to the 

 other alternative which now seems strange,' that all the atoms of an 



'Compare .Aston's historical review {Isotopes, pp. 1-6). C"r<X)kfs very definitely 

 suggested a multiplicity of atomic weights in 1880. 



