The electrical mobilities of multiply-charged nanodrops of the ionic liquid 1-ethyl, 3-methylimidazolium dicyanamide (EMI-N[CN](2)) were accurately measured in air at 20 A degrees C for mass-selected clusters of composition [EMI-N[CN](2)] (n) [EMI+] (z) , with 2 a parts per thousand currency sign n a parts per thousand currency sign 369 and 1 a parts per thousand currency sign z a parts per thousand currency sign 10. We confirm prior reports that the mobility Z of a globular ion of mass m is given approximately by the modified Stokes-Millikan law for spheres, Z = Z (SM,mod) (d (m) + d (g) , z, m), where d (m) = (6m/pi rho)(1/3) is the nanodrop mass-diameter based on the density rho of the liquid (corrected for the capillary compression and electrostatic deformation of the nanodrop), and d (g) is an effective air molecule diameter. There is however a measurable (up to 7 %) and systematic z-dependent departure of Z from Z (SM,mod) . As theoretically expected at small epsilon (*) , this effect is accurately described by a simple correction factor of the form Z/Z (SM,mod) = delta(1 - beta epsilon (*)), where kT epsilon (*) is the potential energy due to the ion-induced dipole (polarization) attraction between a perfectly-conducting charged nanodrop and a polarized neutral gas-molecule at a distance (d (m) + d (g) )/2 from its center. An excellent fit of this model to hundreds of data points is found for d (g) a parts per thousand 0.26 nm, beta a parts per thousand 0.36, and delta a parts per thousand 0.954. Accounting for the effect of polarization decreases d (g) considerably with respect to values inferred from earlier nanodrop measurements that ignored this effect. In addition, and in spite of ambiguities in the mobility calibration scale, the measured constant delta smaller than unity increases Millikan's drag enhancement factor from the accepted value xi (m) a parts per thousand 1.36 to the new value xi a parts per thousand xi (m) /delta a parts per thousand 1.42 +/- 0.03.
