1. Direct Evidence of Downward Refraction of Electro-Magnetic Waves;Appleton,1925
2. A Test of the Existence of the Conducting Layer;Breit;Physical Review,1926
3. Wireless Telegraphy;Fleming;Encyclopedia Britannica,1902
4. On the Elevation of the Electrically-Conducting Strata of the Earth's Atmosphere;Kennelly;Electrical World and Engineer,1902
5. Telegraph Theory;Heaviside;Encyclopedia Britannica,1902