| This early twentieth-century apparatus by Max Kohl of
Chemnitz, Germany, was used to show the magnetic field line configurations
around current-carrying wires. Iron filings scattered on the upper surface
aligned themselves along the magnetic field lines set up by currents in
the wires. Various combinations of parallel and anti-parallel currents
were possible by connecting the leads from the current source to the various
The marble base is typical of Kohl apparatus built after 1900.
The apparatus in in the collection at the University of Cincinnati physics department.