Velocity distribution of photo-electrons excited by soft x-rays.— The apparatus was similar to that used in the magnetic analysis of β rays. Soft x-rays excited by primary electrons with 150 to 1500 volts energy, fall on a radiator of W, Pt, Al, etc. The photo-electrons emitted in a plane approximately normal to the uniform magnetic field acting, each travel in a circle with a radius proportional to the speed; those of a given speed which pass through two fixed slits strike a photographic plate, after describing a semi-circle, along a line depending on their speed, thus giving a spectrum. The plates each show a sharp line with a considerable amount of energy right at the hν limit corresponding to the energy of the primary electrons. A band due to electrons which had lost from 4 to 11 volts in coming out of the radiator, was also observed. These lines and bands indicate that free or loosely bound electrons are more readily ejected than internal electrons by soft x-rays. However, other lines were obtained due to electrons from various levels of the radiator atoms, with energies diminished by amounts corresponding to the critical potentials. Critical potentials obtained by magnetic analysis of photo-electrons.—For aluminum radiator: L2L3, 70 volts; L1, 80 volts. For silver: N1, 134 volts; M6, 365-370 volts. When the target for the primary electrons got covered with tungsten oxide, x-rays corresponding to jumps between N and O levels produced photo-electrons of corresponding energy. In this way the following characteristic lines in the N spectrum of tungsten were observed: N3O5, 410; N2O4, 482; N1O3, 560; N5O3, 305; and N4O2, 312, all in volts. N4O6 is missing, indicating that the O6 level is not occupied. All the values agree well with the Bohr theory predictions and with other results.