Wordsworth’s autobiographical Prelude traces ‘the growth of the poet’s mind’ from infancy to adulthood. Fuelling this growth in its various phases is an energy that Wordsworth most often calls ‘passion’, beginning with the infant’s attachment to the intertwined figures of mother and nature and taking other forms over the course of his life: the ‘troubled pleasure’ of the boy who intrudes upon nature’s quietness, the thrill of fear or conquest when he ventures to new heights or pushes beyond familiar boundaries. Passion drives the youth to depredations of nature and is redoubled by the sublime power with which nature’s reaction works on his imagination afterwards. Intense, unnameable passion also attends traumatic experiences such as the death of parents, the bewildering entanglements of sexual desire and revolutionary enthusiasm, the fear of betrayal. In these seemingly diverse realms of experience, passion is the energy that animates the dynamic interchange between the developing consciousness and the world. In the Preface to Lyrical Ballads, Wordsworth connects passion to ‘the pleasure which the mind derives from the perception of similitude in dissimilitude and dissimilitude in similitude’. Pleasure feeds passions as diverse as sexual appetite and metrical language, a complex, sensitive instrument that not only expresses passion and registers its effects but also reacts to it, influences its direction and regulates its intensity. Metre is (to adapt Keats’s notion of the ‘pleasure thermometer’) a passion thermostat.