Page "Atom" Paragraph 23

The Stern – Gerlach experiment of 1922 provided further evidence of the quantum nature of the atom.

When a beam of silver atoms was passed through a specially shaped magnetic field, the beam was split based on the direction of an atom's angular momentum, or spin.

As this direction is random, the beam could be expected to spread into a line.

Instead, the beam was split into two parts, depending on whether the atomic spin was oriented up or down.