Extremely low frequency (ELF) electromagnetic wave propagation was investigated by measuring the amplitude of a CW signal transmitted from the Sanguine site in North Carolina to receiving sites located in New York State, Labrador, and Iceland. The attenuation factor α and the reciprocal of the excitation factor

were determined. Data for daytime, nighttime, and sunrise transition paths were obtained. The attenuation factors obtained for 78 and 156 Hz are compared with the value of α obtained from measurements of atmospherics. The attenuation values at 78 Hz of 1.29 and 1.01 dB/1000 km, and a value of 0.75 dB/1000 km at 45 Hz, obtained by interpolation of results of this and other experiments, were used in Sanguine systems analysis.