Quote by Johannes Stark
We can in fact first place the beam of rays of moving positive atomic ions in a plane perpendicular to the axis in which we see the spectral lines emitted by them.
Summary
This quote suggests that it is possible to align a beam of positively charged atomic ions in such a way that it lies in a plane that is perpendicular to the direction we observe the emitted spectral lines. In other words, it implies that we can manipulate the trajectory of these ions to achieve an orientation that facilitates the study and analysis of their emitted light.