An apparatus is described for measuring relative field intensities of wireless waves of the order of 20 metres, and the results of a series of measurements taken with it on wavelengths of approximately 25 metres for distances of from 200 ft. to 60 miles from the transmitter are shown as“Intensity/Distance” curves. For distances greater than 2 miles the decrease of intensity is found to be approximately proportional to the inverse square of the distance as predicted by the theory of Sommerfeld. For shorter distances, however, the curves are much straighter than predicted by theory. This is attributed to penetration of the waves to layers of higher conductivity below the surface. This is supported by the increase in the variations in attenuation with change of surface observed on a wavelength of 18 metres and by measurements on the “tilt” of the electric vector of the wave-front.In all cases, marked changes in intensity and attenuation were found to occur with apparently slight changes of surface and slope of the ground.