  The small amplitude-to-thread ratio helical configuration of a vortex
filament in the ideal fluid behaves exactly as de Broglie wave. The
complex-valued algebra of quantum mechanics finds a simple mechanical
interpretation in terms of differential geometry of the space curve. The wave
function takes the meaning of the velocity with which the helix rotates about
the screw axis. The helices differ in type of the screw - right or left-handed.
Two kinds of the helical waves deflect in the inhomogeneous fluid vorticity
field in the same way as spin particles in the Stern-Gerlach experiment.
