If there is a high density of ambient neutrinos—a "neutrino sea"—then on the conventional weak-interaction theory two types of possibly measurable effects exist. In one the spin direction of a transversely polarized moving electron rotates in field-free space. In the other the motion of the earth creates a torque on a ferromagnet.

• Received 28 May 1974

DOI:https://doi.org/10.1103/PhysRevLett.34.110