Adrian and Matthews confirmed Berger's findings in 1934 by recording their own EEGs using a cathode-ray oscilloscope.
From the en.wikipedia.org
After patiently accumulating the muon data for two months-the time necessary to get statistically valid readings-the computer will spew it all out into a cathode-ray oscilloscope.
From the time.com
The cathode ray tube made possible the oscilloscope, an early electronic device that can produce images that are easily associated with sounds from microphones.
From the en.wikipedia.org
Once this was solved the equally difficult problem of actually seeing the fleeting signal became obvious, which he solved with the use of a cathode-ray oscilloscope with a long-lasting phosphor.