We present an experiment designed to study magnetohydrodynamic effects in free surface channel flow. The wide aspect ratio channel ͑the width to height ratio is about 15͒ is completely enclosed in an inert atmosphere to prevent oxidization of the liquid metal. A custom-designed pump reduces entrainment of oxygen, which was found to be a problem with standard centrifugal and gear pumps. Laser Doppler velocimetry experiments characterize velocity profiles of the flow. Various flow constraints

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... gate secondary circulation and end effects on the flow. Measurements of the wave propagation characteristics in the liquid metal demonstrate the surfactant effect of surface oxides and the damping of fluctuations by a cross-channel magnetic field.