Focusing on the historical conjuncture at the turn of the twentieth century, this dissertation examines how theorists in the humanities and social sciences were engaging with energetics and thermodynamic theory in their work. Following the radical developments of nineteenth-century physics, philosophers, sociologists, and literary authors reconceived "non-material" phenomena (mind, society, culture) as part of the natural world through related concepts of energy, force, vibration, and rhythm. An energetic materialism emerged in which theorists reimagined matter as energy and contended with the dynamic relationships this ontology implied. While dynamic and developmental accounts of nature are often associated with evolutionary theory in the nineteenth century, this study demonstrates that the science of energy contributed equally to a metaphysics of transformation. Both philosophical and literary naturalism are considered in this analysis with a focus on Henri Bergson's theory of mind and matter, Emile Durkheim's theory of the social, Henry Adams's theory of history, and Jack London's aesthetics of force and rhythm. In each case, important developments in twentieth-century thought emerged as revised notions of matter and interaction were elaborated in a new discourse of energetic materialism.