Maurice Davies has identified the whole sequence of notes and diagrams running from folio 15 verso to folio 18 verso (D40670, D07381, D07382, this page and D07383–D07386) as taken from John Hamilton, Stereography, or, a Compleat Body of Perspective, in All Its Branches, London 1738.1 Turner could have consulted the copy at the British Museum (since transferred to the British Library, London).
Andrea Fredericksen has noted that the diagrams here, from Hamilton’s plate 18 figures 55 (the line) and 56 (the more complex figure below), inform Turner’s perspective lecture diagram headed ‘Hamiltons Harmonic Proportions’ (see entry for Tate D17133; Turner Bequest CXCV 162).
The source diagram includes more letters than Turner’s version, relating to Hamilton’s complex explanation, transcribed on folio 16 verso opposite (D07382). The subsequent lecture diagram does not retain this lettering, and appears incomplete and inverted compared to the version here.
Davies 1994, p.288.