This depiction of reflecting metal spheres was made in connection with Turner’s lectures as Professor of Perspective at the Royal Academy. In Lecture 5, Turner discussed reflection and refraction, or ‘reflexies’, and their relationship to light and shade, which he illustrated by diagrams of globes, some made of polished metal and others, presumably of glass, half-filled with water (see for example Tate D17148, D40024–D40026; Tate CXCV 177a–d). Here, on the left, Turner shows light from three windows, reflected on a polished metal sphere, while on the right he investigates these reflections in and between a pair of spheres. Turner clearly refers to the drawings in a manuscript used for lecturing in 18111 but has not marked them with his usual reference number. Sketches of the globes can be found in Turner’s first draft of the lecture (private collection). In his text, Turner observes how, indoors, light can be manipulated and shadows ‘dissipated’. Commenting on his friend John Soane’s fascination with light and shade and his various architectural devices for controlling them, Helen Dorey speculates that Turner’s ideas and images helped to inspire features like the convex mirrors Soane installed in his house in Lincoln’s Inn Fields. Soane was present when Turner gave Lecture 5 in 1812. (http://www.tate.org.uk/art/research-publications/jmw-turner/joseph-mallord-william-turner-lecture-diagram-reflections-in-a-single-polished-metal-globe-r1136761)