252 



SCIENCE. 



[N. S. Vol. IV. No. 87. 



It seems to me, then, that the exact quan- 

 titative similarity of the spectra of these 

 elements shows that they are not com- 

 pounds one of another, subject to the great 

 chemical law of the addition of undivided 

 parts ; and that also the magnitudes of the 

 small and well determined atomic weights 

 differ from the values hitherto suggested by 

 applying the law of the addition of un- 

 divided parts, and differ by five, ten and 

 fifteen times the greatest experimental error 

 we can reasonably assume. 



So the citadel which defends the secret 

 of the atom cannot be taken by way of 

 Prout's hypothesis. We have carried on 

 the assault for eighty years, and we are 

 now satisfied that the way is blocked; we 

 tried to breach, not a wall, but the solid 

 mountain itself. "We shall doubtless learn 

 the structure of the atom, but we cannot 

 learn it in the way we hoped. This chap- 

 ter in our study of the nature of atoms has 

 been fully ended. 



If Prout's hypothesis cannot serve us 

 you will doubtless ask what other ways are 

 open by which we may learn something of 

 the structure of atoms. To answer is diffi- 

 cult; to answer adequately is impossible. 

 Perhaps I may mention four lines in which 

 it has been hoped by some that the desired 

 advance could be made, and may indicate 

 what it is reasonable to expect of each. 



One of these indications of a possible 

 source of knowledge as to the structure of 

 atoms was suggested by certain chemical 

 observations on some of the rare earths. 

 My brief explanation will not do justice to 

 the conception of the eminent chemist who 

 investigated the phenomena. As I have 

 said, the atom is something which, as a 

 matter of fact, remains undivided in all 

 chemical changes. Most atoms seem to re- 

 sist every force which we can apply. But 

 it is possible that the amount of resistance 

 which they can offer may vary greatly ; it 

 may be that in the case of some elements 



the resistance is such that in some reactions 

 the atoms remain undivided, and not in 

 others. From the study of such cases, if 

 there are such, we might expect much help. 

 Now, in the case of the common and well 

 studied elements, the occurrence of such 

 cases has not been suspected ; but some of the 

 rarer elements, examined by a process which 

 is frightfully laborious, have exhibited phe- 

 nomena which suggest, as a hypothesis to 

 be further studied, such a subdivision of 

 atoms. But it is probable that we have 

 mixtures of distinct elements which we do 

 not yet know how to separate from each 

 other by simple analytical processes. This 

 chapter, we may fairly presume, will be 

 valuable; but not because it will tell us 

 anything new about the structure of atoms. 



Certain spectroscopic phenomena have 

 suggested that some elements may be de- 

 composed by the action of a high temper- 

 ature. For instance, it has been thought not 

 impossible that, at the temperature of the 

 electric arc, potassium compounds quite free 

 from sodium should begin to show the spec- 

 trum of sodium, because at this tempera- 

 ture potassium is decomposed so as to pro- 

 duce sodium. This hypothesis has been 

 carefully investigated ; in part, by the ac- 

 complished physicist who is its author ; in 

 part, at his suggestion and invitation. It 

 is found that, if years are given to the 

 preparation of potassium compounds free 

 from every trace of sodium, then it is im- 

 possible to obtain from them any phenom- 

 ena suggesting a decomposition into so- 

 dium. Here, again, the new chapter, as 

 far as it relates to the structure of the 

 atom, is likely to be but short. 



A third suggestion did not rest upon any 

 observed chemical phenomena, but was a 

 purely intellectual creation. This is the 

 hypothesis that atoms are vortex rings in a 

 frictionless fluid. It belongs to the mathe- 

 matical physicist, rather than to the 

 chemist, to discuss this interesting sugges- 



