Nature is a short essay by Ralph Waldo Emerson published anonymously in 1836. It is in this essay that the foundation of transcendentalism is put forth, a belief system that espouses a non-traditional appreciation of nature. Recent advances in zoology, botany, and geology confirmed Emerson's intuitions about the intricate relationships of Nature at large. The publication of Nature is usually taken to be the watershed moment at which transcendentalism became a major cultural movement.
Henry David Thoreau had read «Nature» as a senior at Harvard College and took it to heart. It eventually became an essential influence for Thoreau's later writings, including his seminal Walden. (Summary excerpted from Wikipedia by Neeru Iyer)