The reason that the oscilloscope that we know today exists is the invention of the cathode ray tube. These tubes are instrumental in the scopes. Braun invented the scope, almost as a curiosity as much as a tool. Two years after the invention, Jonathan Zenneck added beam-forming plates to the tube and utilized a magnetic field along with it for “sweeping the trace”. Within a decade or two, the devices became much more common in the lab. The only problem was that the cathode emitters and the vacuum were not as stable as many would have liked. Of course, over the years, as technology advanced, they became much better.
An interesting piece of the history of the oscilloscope is that it was once quite common to see them as props in television and in the movies. They were stand-ins that represented scientific equipment in the lab. It was actually quite common to see them in the 1950s and 1960s. The old television show The Outer Limits actually made use of the device in their opening credits.