Kenneth Martin?s series of `Screw Mobile? works, developed from 1953, incorporate a vertical rod with bars attached to it at regular intervals. The distance between the bars was determined by a system called the Fibonacci sequence. This is a pattern found in nature, where each number is the sum of the previous two. It has been used by artists for many years to determine proportions, and was of particular interest to Constructivist artists. Martin wrote that a mobile `can enliven our consciousness of environment, moving as it does in our space and casting its moving shadow.? As the mobile rotates, the optical movements which occur as a result of flickering shadows and light reflecting off the polished surface, are similar to those achieved by Kinetic Artists such as Bridget Riley.