This book is itself shaped like a river delta. Alexander von Humboldt is its source, and his voyage to South America the catalyst that led to a life of pouring out words. Three-quarters of the book describes his life and explains why he is a lost hero of science. Then the book introduces major thinkers who were influenced by Humboldt: Darwin, Thoreau, Haeckel, Marsh, and Muir. Each of these stories involves travel (if you only consider Thoreau's Walden Pond experience to be a sort of inward parallel to the outward voyages of the other four). Wulf especially excels at summing up the impact of Humboldt on these five thinkers with economy and vivid description.
I wish there had been more about where Humboldt's ideas came from. The book focuses on the generation before Humboldt, and it's implied that the advances in travel technology led to the advances in thought (though it would have been interesting to explore this angle a little more, come to think of it). I want to go farther back, to the Greeks, because Humboldt's conception of nature seems awfully Stoic in its composition, and I wonder how much of his ideas had been around since the ancients and how they were carried through to him. Where did Humboldt get his style, and especially this vision of interconnectedness? I want to go deeper, and I could have traded some of the early detail about Humboldt's outer life for more on his inner life.
Also, now that I'm finished with the book I'm left with an interest in reading more of Humboldt, but I don't have a specific "in" to his writing. Part of his forgottenness is that he doesn't have the singular masterpiece that is Origin of Species or the vivid, short articles like Muir wrote. And why is that? Are we just too far removed from Humboldt's time, or is it because he wrote in German? Well, we still remember Goethe more than him. I'd like to think about why.
But these questions arise precisely because this is a good story about a little-appreciated chapter of history. Like the river delta, it opens up into an ocean.