Magnetic Field Visualization

Thinking about springs to apply downforce on plotting pen holders suggested magnets, so I extricated some neodymium bars from my collection of power toothbrush heads:

Magnets - single
Magnets – single

A snippet of magnetic field visualization film shows a dipole pattern:

Magnets - single - field visualization
Magnets – single – field visualization

Snapping two of them together in line:

Magnets - in line
Magnets – in line

… produces a quadrupole:

Magnets - in line - field visualization
Magnets – in line – field visualization

Now, if only I had some magnetic monopoles, this whole thing would be easier!