Magnetic Field Around a Current-Carrying Wire
   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 binding posts.
   The marble base is typical of Kohl apparatus built after 1900.
   The apparatus in in the collection at the University of Cincinnati physics department.  

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