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SCIENCE 



[N. S. Vol. XL. No. 1036 



gree of accuracy of the experiments. But one 

 can be fairly confident as to the electrical 

 character not only of the electron, but also of 

 the entire atom, for there is much evidence in 

 favor of such a view and none that is contra- 

 dictory. The conception of a nucleus, as 

 given in the Rutherford theory, is so well 

 verified in the experiments in the deflections 

 of the alpha-particles, the Telocity of the 

 struck atom, and the high frequency spectra 

 and in the splendid use made of it by Bohr's 

 theory, that it will probably remain, suffer- 

 ing but little change in the future. It is 

 reasonable to believe that the charge of the 

 nucleus is a natural atomic unit, supplanting 

 the atomic weight in determining the posi- 

 tion of an element in the Periodic Table, as 

 now understood. This suggested important 

 function of the nucleus charge seems to af- 

 ford an explanation for the existence of 

 " isotopes," or elements occupying the same 

 position in the Periodic Table, possessing the 

 same chemical properties and giving the same 

 spectrum, but exhibiting different radio-activ- 

 ities. Moreover, it is becoming more evident 

 that our conception of the atomic weight as a 

 natural unit is incorrect, that the atomic 

 weight is merely the resulting apparent mass 

 of the atom, or practically of the nucleus, 

 and that this apparent mass is not merely the 

 sum of the apparent masses of the charges in 

 the nucleus considered separately, for the ap- 

 parent mass of a charge is influenced by the 

 proximity of other charges. 



The very valuable theories of atomic struc- 

 ture, especially that of Bohr, can not, of course, 

 command one's complete confidence. Indeed, 

 Bohr's theory has been extended to but a par- 

 tial investigation of the simplest elements 

 and does not pretend to be complete. It pos- 

 sesses great interest because it is a relatively 

 simple effort to account for the exceedingly 

 complex functions of the atom. At the pres- 

 ent stage of development of this theory its 

 chief faults are the questioned validity of its 

 assumptions, its lack of uniqueness, and the 

 impossibility of extending it to complex 

 atoms. The question of the validity of the 

 assumptions involved should not be taken too 



seriously, for any assumptions that will lead 

 to an agreement of theory and experiment will 

 be welcome. The lack of uniqueness need not 

 be a matter of immediate concern, for experi- 

 mental facts at the present time go far be- 

 yond any suggested theory. There is, how- 

 ever, a strong contention on the part of 

 Nicholson that the present theory of Bohr 

 can not be extended to more complex atoms 

 without marked modifications in the present 

 assumptions. But the' theory is a remarkable 

 contribution even if it does no more than ex- 

 plain many facts known in the case of the 

 simplest elements. When one contemplates 

 the narrow scope of even this brilliant theory, 

 what a limitless field for research seems 

 ahead! Fortunately, there are at hand a 

 number of methods of investigation that have 

 not yet been fully utilized. Some of the most 

 promising lines of research in this field are 

 the extension of theory into the fields of heat 

 radiation and magnetism and to a larger 

 number of elements, the study of high-fre- 

 quency spectra, the scattering of swift /? par- 

 ticles, the production of Eontgen rays by the 

 impact of positive rays, the low temperature 

 characteristics of elements, and the effects of 

 the magnetic and electric fields upon line 

 spectra. To this might be added a long list 

 of experiments which are more indirect, but 

 which, nevertheless, are very important. An 

 illustration is the investigation of the elec- 

 trical and optical properties of selenium 

 crystals, which is now being carried on in the 

 laboratory of this university by Doctors Brown 

 and Sieg. Before all these lines of approach 

 are fully occupied new ones will be found, and 

 there is no indication of a cessation of the 

 attack upon the atom for years to come. 



Where will the investigation end? It will 

 be without end. Notwithstanding the prospect 

 of such a lively attack upon this problem, one 

 can readily appreciate that progress is likely 

 to be made with much difiiculty, taxing all the 

 resources of the physicist and the mathemati- 

 cian. Yet science rarely completes a task be- 

 fore new problems that are more fundamental 

 are found. For example, electricity was first 

 discovered as electrification or strange vari- 



