From the skip distances of radio waves measured in temperate latitudes during 1927 and 1928 the average day ionization is calculated to be at about 200 km above sea level with a maximum electron density of 7.5×105and 5.6×105for a summer and winter day, respectively, which agree with the observed virtual heights from radio echo experiments and the longest wave which at normal incidence pierces through the ionized layer. The ratio 1.33 of summer to winter day electron density agrees with the ratio 1.42 calculated from ionization by the ultraviolet light of the sun. An average night ionization of 2.5×105and 1×105for summer and winter at 160 km is in rough accord with the radio facts as far as they are known, but within limits a more dense ionization at a higher level, or a less dense at a lower level, would accord equally well. The average day ionization for 1927 and 1928 is 6.5×105electrons cm−3which, when compared with the value 4.3×105calculated from the skip distances of 1923 and 1924, shows thatthe ionization increased by about 50 percent from minimum to maximum solar activity.