When cathode rays where researched, people tried to deflect the rays by
electric fields.
It was observed that cathode rays could NOT be deflected by external
electrodes.
Therefore Heinrich Hertz said, no this are not particles, this are
longitudinal waves.
He was the most famous scientist at this time and nobody wanted to speak
against him.
What was the problem? If electrodes are outside of the tube, the rays
cannot be deflected, because there is an electron cloud in the tube that
compensates external fields.
It was at this time already reported in literature, that electrodes
inside the tube can deflect the cathode rays but this was not widely
known and ignored, because Heinrich Hertz had spoken.
So the discovery of electron rays was much delayed.
Another story:
When in early 1912 Viktor Hess came up with the discovery of cosmic
rays, he was ridiculed by the great Millikan.
So the discovery was surpressed and ignored.
1924 Millikan himself discovered cosmic rays and claimed priority ;-)
