An experiment is described that was performed in an alkali plasma (Cs) device in order to test the theory of the Farley instability. With υ E×B > Cs (the speed of sound) and νι ≳ ω cι (ν e ≪ ω ce ) wave excitation occurs, the waves traveling normal to the magnetic field B at the υ E×B speed. The perturbations are strongly elongated along the B field lines, with λ∥ ≫ λ⊥. A comparison with theoretical predictions is given for the observed excitation conditions of the instability.