The diurnal variation of the intensity of wireless waves reflected from the ionosphere

An account is given of the diurnal variation of the relative intensity of waves returned from the ionized regions of the upper atmosphere as observed over the early morning period from about 2 a.m. until about 9 a.m. The relative intensity is taken as the ratio of the intensity of the downcoming wave to that of the ground wave. The influence on the intensity of electron-limitation and of absorption-limitation is discussed, in the light of theoretical ionization curves given by Chapman. The experimental observations described show that the magneto-ionic doubling of the echo, which has been observed by Appleton and Builder for the F region, occurs also for the E region. The doublet echo for this region is observed only for a short period of the morning, owing to the fact that the extraordinary ray is very soon totally absorbed.