As impressive as Colquhoun's ability to sell the idea of a publicly funded police force was, his main contribution is recognized as the introduction of crime prevention, or preventive policing, as a fundamental principle to the English police system. His police were to be a deterrent to crime by their permanent presence on the Thames. He arrived at this conclusion by viewing crime fighting as a science, and in utilitarian fashion, attempted to press that science into the service of the national economy. He published two dozen treatises on a variety of social problems, but the most significant is his 1797 "A Treatise on the Police of the Metropolis".