ELECTRONIC MAGNITUDES 321 



steps required to displace the spectrum of the second 

 to coincide with that of the first. The characteristic 

 lines of the hydrogen atom appear displaced in the 

 spectra of the other elements. (This is evidence in 

 favor of the concept of a positive electron which is the 

 nucleus of the hydrogen atom.) Starting with hydro- 

 gen as unity the atomic numbers of a large number of 

 elements have been obtained by the analysis of these 

 and similar experiments. The method offers a pre- 

 cision in excess of that of preceding methods and has 

 definitely established these numbers. 



Earlier experiments indicating atomic numbers 

 made use of the deflection of an a-ray due to collisions 

 (cf . page 314) . Calculations may be made of the charge 

 of the nucleus of a molecule from the scattering of a 

 particles (or of ft particles) in their passage through 

 solids. Using thin films of metals Rutherford l de- 

 termined some atomic numbers which are hi general 

 agreement with more recent values. 



The concept of an electronic constitution of matter, 

 which we have sketched in the preceding chapters, is 

 to-day commonly accepted. Its development has been 

 so rapid that few scientists besides those actively en- 

 gaged in its research have as yet adopted its terminol- 

 ogy and the necessary point of view. In terms, however, 

 of electrons and quanta, the scientific progress of the 

 next few years will undoubtedly be expressed. 



*Cf. Rutherford, "Radioactive Substances and Their Radia- 

 tions." Cambridge University Press, 1913. 



