Nature's Panorama: Thoreau on the Seasons »

"How vain it is to sit down to write when you have not stood up to live," Henry David Thoreau once observed. The American poet, essayist and philosopher certainly held himself to that standard -- living out the tenets of Transcendentalism, recounting the experience in his masterpiece, Walden (1854), and passionately advocating human rights and civil liberties in the famous essay, Civil Disobedience (1849).