For complex lecture diagrams he normally first carried out a very careful pencil and ink drawing, based on a detailed perspective construction. He then traced the outlines of the drawing and added a simplified version of the main details of the construction to give the lecture diagram. He sometimes enlarged the tracing, possibly using a pantography, or possibly the eye. Even in the latter case he normally kept the viewpoint in exactly the same position. In addition to the lecture diagram showing the construction, he sometimes also prepared a watercolour of the results, also based on the tracing. For Diagram 36 [Tate
D17050; Turner Bequest CXCV 80], he seems to have begun to follow his normal procedure: there is [this] carefully prepared pencil construction, a watercolour based on a tracing made from the drawing (and also numbered 36) [Tate
D17052; Turner Bequest CXCV 82] and a further tracing overlaid with some details of a perspective construction (Tate
D17051; Turner Bequest CXCV 81). However, the latter was abandoned incomplete (the partially shown construction appears to be incorrect in yet another way). The diagram Turner eventually completed [Tate
D17050] is not based on [this] initial pencil drawing. The angle of view of the building is different and it appears to have been drawn free-hand, possibly based on the small sketch in the first draft of the lecture.
1 Several of the lines are not straight and the sides of the building do not recede accurately to the (incorrect!) vanishing points.
2
