Quote by Johannes Stark
Thus at the beginning of 1906 it seemed to be established that the emitters of the spectral series of chemical elements are their positive atomic ions.
Summary
This quote suggests that by the start of 1906, it was widely accepted that the sources of the spectral series observed in chemical elements are the positively charged atomic ions of those elements. In other words, the emission of specific wavelengths of light by elements was believed to be a result of the positively charged ions (atoms with missing electrons) of those elements. This understanding furthered scientific knowledge in the field of spectroscopy, which involves studying the interaction between matter and electromagnetic radiation.