Percy Grainger’s 1935 composition, Free Music No. 1, written for string quartet, but adapted in 1937 for four theremins, is notable not just as an early realisation of the composer’s Free Music ideas, but also because it introduced a form of graphic notation quite unlike anything composers had previously employed. Referencing William Hogarth’s concept of the ‘Line of Beauty’, Grainger would use similar notation systems in the control mechanisms of his Free Music machines of the 1940s and 1950s. His experiments were among the first examples of the use of notation as a form of visual music in and of itself. This chapter explores Grainger’s work in the context of the technological development of parallel notation systems in the fields of ethnomusicological transcription and psychological studies in the early decades of the twentieth century. In particular, Milton Metfessel’s system of phonophotography, and the work of psychologist Carl Emil Seashore, which sought to visualise the phonetic and prosodic elements of speech and song, will be shown to intersect with, and inform, Grainger’s own developments in notation. By considering a range of documentary and media sources, this chapter sheds new light on the inter-relations between apparently disparate archival material.