Three years before Frankenstein was published, Mary Shelley traveled through Europe. While in Germany, she passed near Frankenstein Castle, which may have influenced her novel. The castle was home to Johann Conrad Dippel, an alchemist who created a tar-like substance called Dippel’s Oil. Folklore about Dippel’s experiments possibly inspired Shelley, though she never mentioned this in her journals.

The novel Frankenstein, or The Modern Prometheus by Mary Shelley was published in 1818. Shelley started writing the story when she was...