34 JOUKXAL OF THE MiTCIIELL SoCIETY [July 



an atom in the neutral state determines the place of the ele- 

 ment if hydrogen has one electron and one nuclear unit 

 charge, helium two electrons and two nuclear unit charges, 

 etc. 



The direct method then is a comhination of the work of 

 Bragg, Barkla and Sadler, and Moseley. Making use of the 

 work of those first mentioned, Moseley photographed the 

 spectra ol)tained by the cathode-ray bombardment of a num- 

 ber of elements, the X-rays thus produced being reflected and 

 defined from a crystal face. The frequencies of the vibra- 

 tions could be determined and this frequency w^as found pro- 

 portional to the square of the atomic number. That is, there 

 was a definite shifting in the direction of shorter wave-length 

 in the sj^eetrum of an element from that of the one next above 

 it in the list. 



The graphic representation of the system has never been 

 satisfactory in spite of the many efforts to solve it. It is es- 

 pecially difficult to bring out the facts by any representation 

 on a plane surface. The faults of the ]\fendeleeff table can 

 readily be seen, and they make it very desirable to secure a 

 better mode of expression. And yet it is difficult to use the 

 three dimensions of space so that the average student can 

 grasp the whole. Soddy's leimiiscate curve certainly has its 

 good points. This may be compared with the arrangement 

 of jRydberg. It can not be claimed yet, however, that the law 

 or laws underlying this system are known and well under- 

 stood, and until such time a complete and satisfactory graphic 

 representation is scarcely to be expected. "We can agree at 

 least that progress is being made toward such an understand- 

 ing. 



Chapei. Hill, N. C. 



