Johannes Stark (1874-1957) demonstrates that strong electric fields will split the Balmer spectral line series of hydrogen. The Stark effect is the electric analogue of the Zeeman effect where a spectral line is split into several components due to the presence of a magnetic field.
Editors. "The Stark effect posited". The Literary Encyclopedia. First published 01 May 2009
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6438, accessed 24 June 2016.]