This thesis explores representations of crowd behaviour in prose writing of the late eighteenth and early nineteenth century in Britain. I argue that accounts of the crowd from a broad range of contexts, genres and political prejudices are united by a common intuition that the peculiar qualities of collective behaviour are provoked by sympathy. Sympathy is a ubiquitous term in eighteenth-century studies, but recent accounts of its political application tend to make it an index of mutual approbation and social cohesion. I argue instead that sympathy is a mode of transmission, a medium for the unregulated political energies that make democratic politics a profound worry for commentatorso f all political persuasionsd uring this period. The model of sympathy on which this study draws is a physiological rather than a moral or emotional one. Sympathyh ad long been associatedw ith quack medicine,b ut during this period it becomes a legitimate medical term for the process through which disorder in one organ of the body is instantaneously transmitted to another distant organ, or throughout the whole body. Though the cause of this phenomenon is often attributed to the nerves, physiological sympathy retains its occult overtones, and is never granted categorical explanation. My work demonstrates how this model of sympathy is applied to the behaviour of crowds in the philosophical, political, literary and periodical prose of the period, reaching greatest intensity at periods of social and political unrest. I argue that the threat of the crowd catalysed by sympathy produces surprising continuities between writers of contrasting political views. While reactionary commentators find it easy to denounce the mob, reformers are often forced to agree that that sympathetic communication makes the crowd ultimately resistant to control. But writers of all political persuasions also attempt to find a positive application for the language of collective sympathy, with varying degrees of success. In this thesis I argue the need to reconsider the understanding and applications of sympathy during the long eighteenth century, to give full consideration to its dynamic social and political function. In addition, I assert the significance of accounts like these to the ongoing analysis of `crowd psychology'. Eighteenth-century descriptions of the crowd in terms of sympathy resonate strongly with contemporary accounts of collective behaviour, demonstrating the extent to which questions raised by commentators at this period still remain to be answered. In chapter one I discuss various investigations of physiological sympathy in eighteenthcentury medical writings, and show how sympathy becomes connected in popular medical texts with electrical and quasi-electrical phenomena, including animal magnetism. I show how these phenomena were explicitly associated with mob behaviour in accounts of the Wilkesite agitations of 1768-1770. Chapter two addresses the representation of revolutionary crowds in the writings of Edmund Burke, Helen Maria Williams, Mary Wollstonecraft, William Godwin and John Thelwall during the 1790s. I argue that though Burke is forced to revise his conception of sympathy as an emotional force of social cohesion in the wake of the revolution, he is less troubled than his antagonists, for whom sympathetic transmission disrupts any appeal to rational enlightenment. Only Thelwall, I argueoffers a solution to this iirp sse by embracing the physical basis of sympathetic connection. Chaptert hree examinesr epresentationso f collective behaviouri n the periodical press during the years 1816-1819. I show how a vibrant cheap radical press and a concertedc ampaigno f massp olitical protest transformed understandingsth e influence of sympathyo n collective political behaviour.W hile the `respectablep' ress,r eformist as well as conservative, represents the crowd as unruly rabble, cheap radical publications unsettle this judgement by articulating voices from within the crowd. Despite their commitment to the diffusion of knowledge, these journalists exploit the crossover between the spread of reason and the sympathetic diffusion of physical and emotional energies. In chapter four I address two attempts to reclaim the language of sympathy for cohesive, even loyalist political ends. Dugald Stewart's analysis of `sympathetic imitation' makes sympathy the primary stimulus for collective action but refuses to draw the usual reactionary conclusions. A more profound break with condemnations of collective sympathy comes in the work of Robert Southey, David Wilkie, William Hazlitt and Thomas De Quincey, who all present sympathy as a patriotic force, by associatingit with national systemso f communication such as the mail. However, in the wake of further developments in communication, this positive appropriation of sympathy is necessarily short-lived