So I the biography of Darwin that I was reading made mention a few times of the John Herschel fellow, so I thought I'd do a New & Hot on him and his influence on Darwin.
John Herschel was primarily an astronomer, and also a wildly popular scientist back in the day (the day being the first half of the 19th century). He was in fact so popular that he moved to South Africa to get away from the mobs of fans. Ok that's a little bit of an exaggeration. But not much- he said he was quite happy to leave the pressure of living in England. The main reason he was there, though (and why Darwin and Fitzroy could stop in and say hi to him on their way back to Britain) was to study the stars of the Southern Hemisphere. While he was in South Africa though, he and his wife decided (as people from this time period so often seem to do, because they were just so ridiculously multi-talented) to take up botany, making drawings of the local plants using a combination of new photography techniques and technology. He was also like Humboldt a little bit, it turns out, in that he advocated doing science by carefully collecting data, recording observations, and then using inductive reasoning to come up with theories to explain them. I mean, this is (I'm pretty sure) how we do science nowadays, but I guess back then it was like a big leap or something. And Darwin was affected by Herschel's thoughts on this subject as well. Herschel also read Lyell's Principles of Geology, and his quote that Darwin used about the "mystery of mysteries" was actually from a letter that Herschel sent to Lyell. Darwin might also have gotten it while they were hanging out in South Africa, though.
Anyway, Herschel seems like a pretty interesting guy. Darwin was buried near him in Westminster.