Design and performance of magnets in the automatic telephone
A 1912 undergraduate electrical engineering thesis by Don Llewelyn Hays and Christian Bernhard Thvedt at the University of Illinois, submitted to faculty examiners and reporting tests on electromagnets used in automatic telephone switching. Its plates are pen-and-ink measured drawings of magnet cores, armatures and pivoted levers, a laboratory pull-test rig with beam balance and weights, a horseshoe magnet with wound coils, and hand-lettered plotted curves on ruled graph paper.
