Core-less induction coils in telephone service
An undergraduate engineering thesis on core-less induction coils for telephone circuits, written by Claude E. Smith and Walter M. Stewart at the University of Illinois in 1907. Its plates are sparse pen diagrams on pale paper, each headed by a Roman numeral: single and concentric circles, pairs of ruled horizontal bars, and a plain cross, usable as geometric marks, diagram furniture, or spare page layouts.
