 He explored the mathematical basis for control stability, and progressed a good way towards a solution, but made an appeal for mathematicians to examine the problem.The problem was examined further in 1874 by Edward Routh, Charles Sturm, and in 1895, Adolf Hurwitz, all of whom contributed to the establishment of control stability criteria.In subsequent applications, speed governors were further refined, notably by American scientist Willard Gibbs, who in 1872 theoretically analysed Watt's conical pendulum governor.