Later Years: 1851–1862
In 1851, Thoreau became increasingly fascinated with natural history and travel/expedition narratives. He read avidly on botany and often wrote observations on this topic into his journal. He admired William Bartram, and Charles Darwin's Voyage of the Beagle. He kept detailed observations on Concord's nature lore, recording everything from how the fruit ripened over time to the fluctuating depths of Walden Pond and the days certain birds migrated. The point of this task was to "anticipate" the seasons of nature, in his words.
He became a land surveyor and continued to write increasingly detailed natural history observations about the 26 square miles (67 km2) township in his journal, a two-million word document he kept for 24 years. He also kept a series of notebooks, and these observations became the source for Thoreau's late natural history writings, such as Autumnal Tints, The Succession of Trees, and Wild Apples, an essay lamenting the destruction of indigenous and wild apple species.
Until the 1970s, literary critics dismissed Thoreau's late pursuits as amateur science and philosophy. With the rise of environmental history and ecocriticism, several new readings of this matter began to emerge, showing Thoreau to be both a philosopher and an analyst of ecological patterns in fields and woodlots. For instance, his late essay, "The Succession of Forest Trees," shows that he used experimentation and analysis to explain how forests regenerate after fire or human destruction, through dispersal by seed-bearing winds or animals.
He traveled to Quebec once, Cape Cod four times, and Maine three times; these landscapes inspired his "excursion" books, A Yankee in Canada, Cape Cod, and The Maine Woods, in which travel itineraries frame his thoughts about geography, history and philosophy. Other travels took him southwest to Philadelphia and New York City in 1854, and west across the Great Lakes region in 1861, visiting Niagara Falls, Detroit, Chicago, Milwaukee, St. Paul and Mackinac Island. Although provincial in his physical travels, he was extraordinarily well-read and vicariously a world traveler. He obsessively devoured all the first-hand travel accounts available in his day, at a time when the last unmapped regions of the earth were being explored. He read Magellan and James Cook, the arctic explorers Franklin, Mackenzie and Parry, David Livingstone and Richard Francis Burton on Africa, Lewis and Clark; and hundreds of lesser-known works by explorers and literate travelers. Astonishing amounts of global reading fed his endless curiosity about the peoples, cultures, religions and natural history of the world, and left its traces as commentaries in his voluminous journals. He processed everything he read, in the local laboratory of his Concord experience. Among his famous aphorisms is his advice to "live at home like a traveler."
After John Brown's raid on Harpers Ferry, many prominent voices in the abolitionist movement distanced themselves from Brown, or damned him with faint praise. Thoreau was disgusted by this, and he composed a speech—A Plea for Captain John Brown—which was uncompromising in its defense of Brown and his actions. Thoreau's speech proved persuasive: first the abolitionist movement began to accept Brown as a martyr, and by the time of the American Civil War entire armies of the North were literally singing Brown's praises. As a contemporary biographer of John Brown put it: "If, as Alfred Kazin suggests, without John Brown there would have been no Civil War, we would add that without the Concord Transcendentalists, John Brown would have had little cultural impact."
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