What is the doppler effect in canal rays

I have to do a write up on Johannes Stark for physics and can't find very much information of the doppler effect in canal rays (part of what he won his nobel prize for).

Could anyone give an explanation? I know what the doppler effect & canal rays are I just don't see how they fit together or how they're worthy of a nobel prize.

cheers

Here is a link to the 1919 Nobel Award presentation speech. You should find what you are looking for there.
http://www.nobelprize.org/nobel_prizes/p…