The microphotometer measures the magnitudes of stars on photographic plates. This type of microphotometer was named after Johannes Franz Hartmann, (1865-1936). Astrophysicist, born in Erfurt, Germany, Hartmann developed measuring methods and standards (standards for wavelengths, microphotometer, method of testing telescope lenses).
Hartmann's biography: http://www.plicht.de/chris/17hartma.htm