The particular feature of the point-to-ring corona has been utilized in order to carry out measurements of the mobility of large positive ions by balancing their drift in a known electric field against a known air flow velocity. The experimental results have provided evidence of ionic-mobility values of the order of 10−6m2/V s. These are typical values of the so-called intermediate ions which normally consist of some 4000 water molecules surrounding singly charged ionized atoms such as H+and Na+. ©1997 American Institute of Physics.