The only experimental work ever published by Albert Einstein was carried out in 1915 in collaboration with Wander Johannes de Haas, who was the son-in-law of H. A. Lorentz. Einstein had long contemplated Ampère’s conjecture in 1820 that magnetism is caused by circulation of electric charge. This Demonstration describes a technologically updated version of the original Einstein–de Haas experiment. A cylindrical soft-iron magnet is supported by a thin quartz fiber attached to a mirror. The magnet is suspended within a solenoid connected to a reversible DC power source. The current is large enough to create a magnetic field strong enough to saturate the cylinder’s magnetization in either direction. If Ampère was right, this should create an angular displacement of the magnet, which can be detected by deflection of a laser beam directed at the rotating mirror.