An experimental study of the Koepsel permeameter
A 1914 technical bulletin from the National Bureau of Standards reporting laboratory tests of the Koepsel permeameter, written for physicists and electrical engineers measuring magnetic properties of iron. The plates are line-drawn magnetization curves on ruled grids with hand-lettered labels, plus a sectional diagram of a magnet yoke with arrows tracing flux paths, useful as instrument schematics and graph furniture.
