Given a scientific question and its correct answer, generate supporting facts for the answer. This supporting fact can be an explanation for the answer to the given question.
Q: Question: Scientists did not actually see viruses until what was invented? Answer: electron microscope
A:
Scientists did not actually see viruses for the first time until the 1930s. That's when the electron microscope was invented. The virus shown in Figure below was the first one to be seen.