One hesitates before any new book on Henry David Thoreau. He is, of course, the equal of Emerson, Dickinson and Whitman as a major writer of the mid-19th century, that magical period once called the American Renaissance. Writers in that period understood that ‘nature is the symbol of spirit’, as Emerson put it, and that ‘every natural fact is a symbol of some spiritual fact’. These classic statements come from ‘Nature’ (1836), Emerson’s seminal essay behind the movement known as Transcendentalism. Emerson believed in ‘correspondences’ – that nature and spirit were deeply connected. Yet whereas he put forward the theory, his younger friend Thoreau found the bright particulars, writing perhaps the finest memoir of the 19th century in Walden (1854).