On the Adamant, the latest endeavor from French documentary filmmaker Nicholas Philibert (The Land of the Deaf, Each and Every Moment, Nénette), is an almost deceptively subtle film. Following staff and clients of a psychiatric day centre on a floating structure in the Siene River in central Paris, On the Adamant combines slow, languid shots of the river (and the city that surrounds it) with interviews and scenes of the centre’s daily activities where patients paint, play…