The torsional strength of wings
This is a 1930 NASA technical report on the torsional strength of aircraft wings, issued through the NASA Technical Reports Server and aimed at aeronautical engineers. The two pictures are structural diagrams: the first shows front, center and rear spar layouts of a wing with lettered bay panels and station numbers along the span, and the second shows top and bottom drag truss frameworks drawn as triangulated lattices. A designer could take from them the clean geometry of crossed diagonals and repeated triangular bays as a graphic pattern.
