Weak gamma-ray ionization currents in air at pressures extending to 193 atmospheres were measured at -76°C and at 96°C. The same apparatus and procedure were used as in the room-temperature measurements, with collecting field intensities from 0.17 to 4500 volts/cm. Under all conditions the current increased with increase of field intensity. At -76°C the current corresponding to a particular intense collecting field has a pronounced maximum in the neighborhood of 60 atmospheres. No such maxima were observed at 96°C. As at room temperature, negative ion currents were found to be greater than the corresponding positives. In their dependence upon temperature and gas density the observed temperature coefficients of the currents agree well with the predictions both of the initial recombination theory and of the columnar theory in the region of low collecting field intensities. They further display the dependence upon field intensity required by the columnar theory. Adopting the assumptions of Gross relative to dependence of the ordinary ion coefficients upon temperature, we modified the coefficient in Zanstra's equation (based upon the Jaffé columnar theory) to correspond to the new temperatures. The result was fairly satisfactory. The theoretical saturation currents so obtained display unexpected relations to gas density. At -76°C the theoretical saturation current has a pronounced maximum at about 90 atmospheres, with some indication of a minimum at about 150 atmospheres. At 96°C the theoretical saturation current values increase very rapidly with increase of pressure at the high pressures.

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