Turner produced this drawing of a transparent globe, along with others of globes made of different materials, for a lecture on ‘reflexies’ (reflections) and their relationship to light and shade, to be given as Professor of Perspective at the Royal Academy. These diagrams are not numbered, but Turner clearly refers to them in a manuscript used for lecturing in 1811.1 As Maurice Davies records, this diagram and three others (Tate D40024–40026) were once on a single sheet. A reference by Finberg to a single diagram numbered 177 of ‘glass balls, partly filled with water’ suggests that the larger sheet was still intact in 1909. Sketches of the globes can be found in Turner’s first draft of the lecture (private collection). For Turner’s discussion of reflecting spheres in Lecture 5, and its possible influence on his friend John Soane, see notes to D17147. (http://www.tate.org.uk/art/research-publications/jmw-turner/joseph-mallord-william-turner-lecture-diagram-reflections-in-a-transparent-globe-r1136762)