274 



SCIENCE 



[N. S. Vol. XLVI. No. 1186 



must have its origin in rapidly oscillating 

 or orbitally moving electric charges whose 

 periods are the same as the periods of the 

 emitted radiation. Further, since spectral 

 lines, except those belonging to bands, were 

 found always to be characteristic of the 

 elements and never of their compounds, it 

 soon became evident that the correspond- 

 ing radiations are of atomic and not molec- 

 ular origin. Hence the natural conclusion 

 that the atoms of all elements, for all give 

 line spectra, are either associated with or 

 consist, in part at least, of electric charges 

 undergoing complete periodic changes of 

 distribution or position '^t the rate ob- 

 viously found by dividing the velocity of 

 any given radiation by the corresponding 

 wave-length, changes, therefore, in the 

 case of green light, at the rate of some six 

 thousand million million per second. Such 

 numbers, of course, are appalling, but the 

 logic is inexorable. 



2. In 1885 Balmer^ announced his re- 

 markable though empirical series formula 

 as applied to the visible hydrogen lines H ^ 

 H „, H and E, : that is 



a formula that has since been found to 

 give with great accuracy the wave fre- 

 quencies of the whole hydrogen series of at' 

 least 35 lines. The same general formula, 

 or some modification of it, such as Eyd- 

 berg's, 





gives with equal accviracy the wave fre- 

 quencies of the lines of many other series 

 of various elements. 



Here, then, was a further important hint 

 in regard to the structure of the atom, but 

 for a long while no one interpreted what it 

 meant. 



1 Ann. dor Pliys., 25, 80, 1885. 



3. In 1897 Lord Rayleigh^ emphasized 

 the fact that the vibrations producing spec- 

 tral series hardly could result from ordi- 

 nary elastic or electric forces of restitu- 

 tion since each of these gives equations in- 

 volving squares of the frequencies — the 

 displacement being expressed in terms of 

 sin t/X its acceleration involves the factor 

 1/X^ — ^while the B aimer and similar for- 

 mulae that so closely follow the lines as they 

 actually occur contain only first powers of 

 this term. 



Although Lord Rayleigh's paper was es- 

 sentially negative in respect to atomic 

 structure, it nevertheless was an important 

 contribution to this difficult subject in that 

 it rendered well nigh untenable certain 

 theories that appeared then to be more or 

 less generally held, namely, all that com- 

 pared the atom to an elastic sphere, paral- 

 lelopiped, or other solid, and those alike 

 that assumed it to be some unknown type 

 of Hertzian oscillator. 



4. In the meantime two other important 

 spectroscopic phenomena were announced 

 that at first seemed to render far more diffi- 

 cult any satisfactory interpretation of the 

 atom and its structure. These were, a, the 

 pressure displacement of spectrum lines, 

 discovered by Mohler and the author' in 

 1895, and, i, the magnetic resolution and 

 dispersion of such lines, discovered by Zee- 

 man* in 1896. 



5. About this same time investigations 

 on electric discharges through gases, and 

 analogous phenomena, became world wide, 

 initiated mainly by the wonders of the X- 

 rays and largely sustained by the frequent 

 stimuli of new discoveries by Thomson, 

 Rutherford, IMadame Curie, and their bril- 

 liant associates. 



Among the many important results of 



2 FUl. Mag., 44, 356, 1897. 



3 Astrophys. Jr., 3, 114, 1896. 

 * Phil. Mag., 43, 226, 1897. 



