Born in Philadelphia in 1898, Calder has utilized a training as a mechanical engineer in the field of sculpture. In his constructions of metal, wire and wood, he concerns himself with the esthetic value of abstract and geometrical forms, as they move through space in varying orbits and shifting interrelationships. Calder sometimes employs motors to keep the parts in motion. More frequently, as in our Mobile, objects are suspended in space from a series of booms. A large, central form resting on three steel rods supports a wire boom, which in turn supports smaller ones. The suspended forms, of red, yellow, blue and orange, are balanced so delicately that the slightest interference with the equilibrium of the system -- a light touch, a breath of air -- causes these forms to alter their relative positions in space.
-Adapted from the Bulletin of the DIA, vol. 26, no. 1 (1947)