Abstract: This invention provides a device for visually displaying magnetic patterns assumed within or recorded on a planar medium, e.g. electrical steel sheet, comprising a transparent plate and a membrane secured to and spanning the plate defining a sealed area therebetween housing magnetic particles suspended in a liquid carrier. A field is applied by permanent magnet(s) disposed around the periphery of the plate or by an energized coil for subjecting said particles to a magnetic field in a direction normal to the plate whereby, when placed in juxtaposition with the planar medium the particles agglomerate to assume positions in conformity with the magnetic patterns.