In this paper on the operation of the water-cycle in meteorology Hutton hypothesized that rain was caused by a mixture of air currents of differing temperatures, either saturated or nearly saturated with moisture. "His Theory of Rain proposes the rule that 'the action and effect of heat and cold' lies at the base of all rainfall. As he says, he seeks to 'form a theory of rain upon that investigated rule, concerning the evaporation and condensation of water' . . . Backed with a considerable array of facts on humidity, temperature, wind currents, and precipitation, Hutton propounds that the amount of humidity in the atmosphere increases proportionally to an increase in the temperature; precipitation occurs where a colder air mass collides with a hotter air mass, thereby cooling it and forcing it to expel its moisture" (Farnsworth, Mediating order and chaos: The water-cycle in the complex adaptive systems of romantic culture [2002] 23-24).  Hutton noted that mountain ranges can cause precipitation by raising and cooling warmer moisture-bearing air and claimed that rain could be predicted scientifically by carefully studying geographical features and wind currents.