In April 1903, in a book-lined study in St John's College, Cambridge, the psychologist W. H. R Rivers and the neurologist Henry Head posed for a photograph (Figure 1). Rivers, on the right, somewhat younger looking and smartly dressed, industriously held a scientific instrument. Head, on the left, bearded, older, sat with his eyes closed, his chin cupped in the palm of his right hand, his face tilted away from the camera, suggesting one lost in reverie. On the table, extended between the two men lay Head's left arm. Scattered around it were a number of laboratory devices for measuring sensation: the pressure-aesthesiometer (for measuring sensitivity to force applied to the flesh), the spring algesimeter (for measuring thresholds of pain), a pitcher of iced water, a box brimming with the softest jeweller's cotton wool and a series of fine wire 'hairs'.1 For this photograph, the two men fashioned themselves into a tableau vivant to illustrate an experiment which took place between 1903 and 1907. It began on 3 April 1903 when Head underwent an operation to sever the radial nerve of his left arm. During the four and a half years that followed, Head and his colleague Rivers tested the gradual and faltering return of sensitivity to Head's hand each week. Their aim was to understand the physiology of sensation which was considered to be 'one of the most obscure regions of neurology' at the time. 3 Head was not alone in regarding self-observation as a technique of the scientific observer, and his method, as I will go on to describe, can be positioned within a tradition of introspection used in experimental psychology in Europe and America between 1870 and 1920. But Head's 'negative attitude of attention' in the laboratory is also reminiscent of modes of aesthetic contemplation he described in the letters and scrap-books that documented his artistic pursuits -trips to art galleries and churches, reading and writing poetry, visits to the opera and, in particular, to the theatre. This article will explore the connections between Head's introspective practice and his descriptions of theatre-going, foregrounding his attempts to produce states of reverie as a technique for self-observation in both.Drawing attention to moments when Head's cultivated state of daydreaming in both theatre and laboratory failed -due to interruptions by others, self-consciousness about being observed, or the distractions of painful sensations -my discussion will explore what Christopher Lawrence and Steven Shapin have called the 'embodied human processes' through which scientific knowledge has been produced, and their 'vicissitudes'. 4 At the same time, by exploring the entwined practices of selfwatching and reverie in psychological and theatrical contexts, this article complements current scholarly debates that address the problems of perception, attention, absorption and theatricality in scientific and wider cultural discourses at the end of the long nineteenth century.