English: Photo of the magnetic field of two bar magnets with unlike poles close together. The magnetic field is made visible in the patterns of a layer of iron filings on a piece of paper laid on top of the magnets. The iron filings are shaped like long thin needles, and orient themselves parallel to the magnetic field lines at each point. From a 1916 physics text. Alterations to image: Changed bluish background to white by adjusting brightness, converted to greyscale, cropped out caption, converted to 24 greyscale PNG.