Stern-Gerlach (1922)

Shot silver atoms through a slit then a magnetic field and observing the splitting on a screen. This is due to the fact that the magnetic moment is collinear with the Spin of the atom. The dual slits implied that the spin is quantized rather than continuous. $\overrightarrow{\mu }=\frac{e}{m_{e}c}\overrightarrow{S},W=-\overrightarrow{\mu }\cdot \overrightarrow{B},F={\mu }_z\frac{\partial B_z}{\partial z}$.

Results showed that spin states are discrete by the dual band of Silver atoms from the spin up and down states.