Natural History Methods & Techniques
What is it that "naturalists" actually did? Pursuit of natural history had become, especially in Britain in the early 1800s, an extraordinarily popular activity. A range of publications, from inexpensive to luxurious productions, supported a broad spectrum of interests, available to every class and level of expertise. Local societies and clubs, libraries and lecture halls, and museums provided access to knowledge. A well-off young man, like Charles Darwin, could engage in such a hobby (or even obsession) for simply collecting with some respectability. An eccentricity such as his "zeal" for collecting beetles might lead, more rarely, to "a strong desire to add a few facts to the great mass of facts in Natural Science" [as Darwin later wrote in his Autobiography], and even the thrill of seeing one's discoveries in print. Most natural history was based on the collection of specimens, then to be described and classified and catalogued, naming new species and arranging their relationships within a taxonomic system. The usual naturalist was not proposing hypotheses and testing theories, but emphasizing a Baconian induction of gathering facts and arranging the results into a settled order.
The emphasis on rigorous empiricism and inductive logic was the lesson from Darwin's Cambridge professor, the botanist John Henslow. He became a mentor and friend, not in the classroom but through his weekly "open house" where members of the University gathered to talk science. Darwin also learned the techniques for collecting plants, preserving the dried specimens, and working out their classification. He acquired some awareness of the geography of variation, in how the same species might vary in different local environments -- though the study of variation was not a driving question in the standard natural history of the 1820s.
As young professors interested in doing and promoting new sciences, Henslow and the geologist Adam Sedgwick co-founded the Cambridge Philosophical Society. Geology also was based on rigorous measurement in the field, leading in the early 1800s to a period of competing theories of geological actions and formations. Darwin acquired some basic skills in fieldwork after graduating, when he was an assistant to Sedgwick on a field expedition. Darwin did not take geology classes with him, but again learned by practice -- how to measure and take notes on profiles and cross-sections, determine strikes and dips, and prepare maps of the surface features and underground structures. He also acquired Lyell's new Principles of Geology, which would become his guide as an investigating and theorizing geologist.
On the expedition of HMS Beagle, Darwin was an energetic collector and observer. Underway at sea, his collecting included dredge and plankton tows (then a new technique) for marine invertebrates. Once collected, specimens could be sorted, possibly identified (aided by the large library of natural history treatises aboard the ship), and preserved for shipment home. From his notes and journals, we can see that he noted ecological assemblages of species, and the change in what was present as they traveled into different environmental conditions. Spending most of the expedition on land, in a variety of islands and across South America, Darwin pursued geological and ecological observations, measurements, and collections. Darwin was emulating Humboldt, making geographic comparisons and climate zones. He was emulating Lyell, mapping patterns and thinking about their underlying natural causes. The expedition gave him something valuable and relatively rare for a naturalist -- broad geographic comparisons made through observation and measurement of a great variety of landscapes and species.