A new method for measuring steady-state nucleation rates on ions in an upward thermal diffusion cloud chamber is described. It provides quantitative measurement of all relevant variables, i.e., temperature, supersaturation, and ion density. Each of these variables, as well as the ion sign and the chemical makeup of the ions, can be readily changed and investigated. Using this technique, it is shown that the nucleation rate is directly proportional to the ion density. It is also shown that there is no dependence of the nucleation rate on electric field strength nor is there a dependence on the ion’s chemical makeup.