SOME CONTEMPORARY ADVANCES IN PHYSICS— X 141 



certain limited set of facts (as the grouping of terms in nuiltiplets) 

 by giving them quahties gra\ely in discord with those attributed 

 to the atom-model for hydrogen; and then they proved themselves 

 surprisingly well able to account for isolated facts of quite a different 

 sort (as the effect of magnetic fields upon atoms). The presentation 

 in these pages is naturally very far from complete; had it been com- 

 plete, it would have filled a book and not an article. But if it had 

 been complete, the eventual impression would have been the same; 

 an impression of confusion, yet of a confusion full of hope. 



For the "Theory of Atomic Structure" is distinguished especially 

 by this, that it is not one theory but a multitude of partial theories, 

 each designed and competent to cover a limited family of the abound- 

 ing data, each struggling to overlap and to absorb the others. It 

 may be compared with a cross word-puzzle or a map-puzzle, in which 

 the beginnings of a solution have been made in half-a-dozen corners 

 and patches, while wide blank areas adjoin and separate them, and 

 some of the partial solutions already entered upon the field may finally 

 yield to others which can be unified into the perfected pattern. Or 

 it may be compared with those maps of polar regions, in which here 

 and there a properly-surveyed island or little strip of coastline emerges 

 from the blankness of the unexplored realms, and some of them are 

 certainly misplaced relatively to the others and will be shifted on the 

 map when all the geography is at length made known. Or it may be 

 compared with the state of a congealing metal, in which a multitude 

 of little crystals have formed themselves about casual nuclei of crys- 

 tallization ; each is oriented in a different way, and when two of them 

 groW' into contact with one another they clash and cannot merge, 

 they stand blocking and thwarting one another. It may be neces- 

 sary to reliquefy them all and make a new attempt to change the 

 formless mass into a single crystal. 



Meanwhile the work is driven forward wuth the fervor of discovery 

 and exploration, in this period which Russell finely called the "Heroic 

 Age of Spectroscopy," and not of spectroscopy alone. Many, though 

 not so many as are needed, are busy with determining the Station- 

 ary States by deciphering the rich and cryptic spectra of some among 

 the numerous unstudied elements — -enormously numerous, taking into 

 account how many kinds of ionized atoms there are; and others with 

 the assembling of new photographs of spectra made under the most 

 varied sorts of excitation, wdth other aids to discriminating the lines; 

 and others with the impressing of electric and magnetic fields upon 

 radiating atoms; and others are engaged in measuring the intensities 

 of lines. Yet other experimenters are determining the magnetic 



