A method previously proposed for a test of the existence of ionization in the upper atmosphere has been developed, and a definite proof of the existence of echoes from the upper regions has been obtained. The echoes are present for 70-meter waves with an 8-mile base near Washington, D. C. The effective height of the layer is between 50 and 130 miles. At times multiple reflections are present. Radio fading is shown to be not only an effect of interference between the ground and the reflected waves, but also to a large extent an effect of the presence or absence of reflected waves. A seasonal variation in the effective height between summer and fall seems to exist. A smaller diurnal effect is also suspected. The height seems greater in the fall than in the summer and greater in the afternoon than in the morning. Effects of wave-length and of location have been studied. A quantitative discussion of the results enables one to eliminate too gradual distributions of electron density. The measured retardation is shown to correspond to a height greater than the actual by amounts differing for various polarizations of the refracted waves.