Stern–Gerlach experiment

1922 physical experiment demonstrating that atomic spin is quantized

In quantum physics, the Stern–Gerlach experiment demonstrated that the spatial orientation of angular momentum is quantized. Thus an atomic-scale system was shown to have intrinsically quantum properties. In the original experiment, silver atoms were sent through a spatially varying magnetic field, which deflected them before they struck a detector screen, such as a glass slide.

From Wikipedia, under CC BY-SA. More on occurri.