The variable speed induction motor
An 1902 engineering thesis on variable speed induction motors by Max Ross Hanna and Charles Dietrich Wesselhoeft, submitted at the University of Illinois and read by faculty examiners. The plates are hand-plotted test curves inked on pale green graph paper, plus a pen-drawn switching diagram with black bar-block coils and hand-lettered captions, giving designers grid textures, thin plotted lines with point markers, and draughtsman's lettering.
