American painter, sculptor, and writer on art, born at South Bend, Indiana, the son of an engineer. In 1913 he moved with his parents to Scotland and he took a degree in history at Balliol College, Oxford, in 1929. Before returning to the USA in 1930 he also studied art at the Ruskin School, Oxford, and under Lhote in Paris. In the USA he taught at various universities, while continuing to keep in touch with Europe through visits. Until he was in his early 40s he was primarily a painter, his work including murals for Olivet College, Michigan, and the Post Office at Selinsgrove, Pennsylvania. In 1949, however, he began to make mobiles, and thereafter he devoted most of his energies to this type of Kinetic sculpture. He worked first in glass and then from 1950 in metal, usually stainless steel. Originally he used simple rod-like forms, then in 1965 he began experimenting with planes based on regular forms such as the rectangle or cube—with ‘emphasis on surfaces rather than lines’. His sculptures are often designed to be situated out-of-doors and usually rely on air currents to set them in motion. He had numerous public commissions in the USA and elsewhere. His writings include the book Constructivism: Origins and Evolution (1967); this was once regarded as a standard work on the subject, although its use of the term would now be regarded as so wide-ranging as to be confusing.