We report a successful experimental test of an interferometer for cold
neutrons using multilayer mirrors. Interference fringes that are anal
ogous to the Brewster's fringes in classical optics have been clearly
observed using the cold neutron beam with a wavelength of 12.6 Angstro
m and a bandwidth of 3.5% at full width at half maximum. The observed
interference fringes demonstrate the coherence of the reflection off t
he multilayer neutron mirror and confirm the feasibility of cold neutr
on interferometry using multilayer mirrors.