Julia invites William to a lecture on the Michelson-Morley experiment. This was was a scientific experiment to investigate a substance called aether, which was long believed to fill empty space. The experiment was done by Albert A. Michelson and Edward Morley in 1887 and later repeated by other scientists with increasing sensitivity. It effectually disproved the aether hypothesis and initiated a line of research that eventually led to the theory of special relativity.
This episode takes place in 1897.
In the beginning of the episode, the newspaper he is reading has the same stories as the newspaper in the opening credits of every episode.