The electron-spin resonance of F centers in potassium iodide is observed at 293°K, 77°K, and 4°K. Addibvely-c~lored crystals of several concentrations and x-rayed crystals show the same resonance with g= 1.970 and a width of 213 gauss at maximum slope. The saturation of the absorption is measured. The resonances of F centers in potassium halides are compared.

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An extended series of measurements has been made to determine the possible variation of W, the energy to make an ion pair in pure argon, with the energy of the ionizing alpha-particle. The ionization in argon relative to the ionization produced by a comparison polonium alpha has been measured for the alphaemitters ThX, ThC, ThA, RaC, ThC. For alpha-particles in this energy region from 5 to 9 Mev, no deviation of W from the average W for the polonium alpha could be found amounting to as much as § percent. This is in marked contrast to the alpha-ionization in air from the work of Stetter. More indirect measurements in the region 1-5 Mev indicate no measurable change in W for alpha-particles in argon, while values derived from the Stetter curve for air show a marked increase of W as zero alpha-energy is approached. Evidence from direct measurements is given to show that the energy to make an ion pair in argon for the Li 7 * ion emitted from the reaction B 10 («,a)Li 7 * is apparently the same as the average for the polonium alpha-particle.

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