322 THE AMERICAN NATURALIST [Vol. LI 



brought us very close to a cancellation of all of the names 

 except one; the demonstration of the existence of par- 

 ticles of negative electricity smaller than any known 

 atom, instead of further complicating the facts of chem- 

 istry, has introduced a hundred simplifications. Mechan- 

 ics, chemistry, optics, and the sciences of heat, electricity 

 and magnetism are rapidly fusing into a single logical 

 system, the ultimate terms of which are minute particles 

 of positive and negative electricity, the ultimate laws 

 those of electro-dynamics, and the ultimate problems 

 those of the structures formed by these particles in space 

 and of the changes which these structures undergo in 

 time. 



This startling progress in physics during the last two 

 decades has not been the product of unadulterate em- 

 pirical research. On the contrary, it has been made pos- 

 sible only by acts of daring speculation, which to certain 

 more orthodox scientists of an earlier period might have 

 seemed inexcusably foolhardy. However, their justifica- 

 tion has often come so quickly and in such unequivocal 

 terms, that methodological critics have been obliged to 

 remain modestly silent. To indulge in a definite and de- 

 tailed account of the structure and behavior of single 

 atoms of hydrogen— particles far beyond the visual range 

 of even the ultra-microscope— may seem no more a scien- 

 tific undertaking than the fabrication of a fairy-tale; and 

 yet when from this account there emerges by inevitable 

 logic a mathematical formula corresponding exactly with 

 the constitution of the complex spectrum of hydrogen, 

 our minds are opened to the possibility that the specula- 

 tion is pointing the way to a fundamental truth.^ This 

 impression becomes especially forcible when we consider 

 that the constitution of this same hydrogen spectrum had 

 for twenty-eight years defied the intellects of the best 

 scientists, and by some had been regarded as incapable 

 of explanation upon any simple hypothesis. 



It is a fact of fundamental logical significance that the 



2 The reference is to the theory of N. Bohr, published in the Philosoph- 

 ical Magazine, 1913, 26; 1, 476 and 857. 



