Iron filings may become magnetized in the presence of a magnetic field, such that each particle acts as a small bar magnet. These tend to cluster together in "strings" that align themselves along the field lines. Here, the filings are encased within a transparent container that is filled with mineral oil, a fluid of sufficiently high density and viscosity that the filings will remain suspended within it for a significant amount of time, yet are still sufficiently free to reorient themselves. Begin by shaking the container so the filings are distributed more or less evenly throughout its volume. You may need to re-shake the container periodically to redistribute the filings