By suspending forms that move with the flow of air, Calder revolutionised sculpture. Marcel Duchamp dubbed these works ‘mobiles’. Rather than a solid object of mass and weight, they continually redefine the space around them as they move. Calder’s subtle balance of form and colour resulted in works that suggest an animated version of paintings by friends such as Joan Miró. This very early example was acquired by Julian Trevelyan when he first got to know Calder in the early 1930s.