Composite permanent magnets, embodying the latest anisotropic alloys, are being used increasingly in equipment for research in many branches of applied physics. Among the advantages are freedom from power supplies, and also constancy of field, when compared with the electromagnet. Flexibility is achieved in the electro-permanent magnet by either reinforcing the permanent magnet field or artificially aging to a reduced value of field strength. Particular applications are for cosmic-ray traps, nuclear magnetic resonance apparatus, mass spectrometers, and β-ray spectrographs; the design of a magnet for the latter purpose being discussed in detail.