Maxwell himself developed the first durable colour photograph in 1861 and published the first scientific treatment of control theory. Control theory is the basis for process control, which is widely used in automation, particularly for process industries, and for controlling ships and airplanes. Control theory was developed to analyze the functioning of centrifugal governors on steam engines. These governors came into use in the late 18th century on wind and water mills to correctly position the gap between mill stones, and were adapted to steam engines by James Watt. Improved versions were used to stabilize automatic tracking mechanisms of telescopes and to control speed of ship propellers and rudders. However, those governors were sluggish and oscillated about the set point. James Clerk Maxwell wrote a paper mathematically analyzing the actions of governors, which marked the beginning of the formal development of control theory. The science was continually improved and evolved into an engineering discipline.