Observations upon the reflecting regions of the atmosphere show that in addition to the reflections from the E, Fl, and F, regions, occasional reflections occur from heights of 50 and 25 (circa) kilometers. This has been called the D region. With a very short pulse (4 to 10 microseconds) and a rapid sweep upon the oscilloscope (18,000 inches per second), a reflecting region has been found within the troposphere. At the present time (summer, 1938) the region is about 1.8 kilometers high. This so-called C region changes its height with the change in weather. It may perhaps be influenced by magnetic storms, sunspots, and chromospheric eruptions.