The paper presents a survey and analysis of field intensity measurements obtained during the years 1937–1939, over the Post Office radio-telephone link between Guernsey and Chaldon, England, on wavelengths of 5 and 8 m. (frequencies 60 and 37.5 Mc./s.). The path between the stations was almost entirely over sea and about 85 miles in length, of which some 36 miles was outside the optical range. The data recorded have been analysed in such a way as to illustrate the general and detailed variations in received signal strength, and the manner in which these are dependent on various atmospheric conditions.The results of the analysis have shown that while the fading of the signals was similar in type on the two wavelengths, there was a difference in the secular variation of the amount of fading on 5 and 8 m. No diurnal or seasonal variation of signal intensity was noted, nor was there any definite diurnal variation in the amount of fading. The fading observed took various forms, ranging from a rapid type in which the changes occurred more or less periodically every three or four minutes, to a slow type of variation extending over one or more hours. The latter type was usually accompanied by a high level of signal intensity interrupted at long intervals by rapid and deep fading lasting from 10 to 30 minutes. The field strength records show a marked correlation between periods of negligible fading and the existence of low atmospheric pressure conditions generally, including lack of appreciable temperature inversion. The occurrence of fog and snow has a similar effect to that due to the prevalence of low pressure.A consideration of these results and of similar data obtained by other workers leads to the conclusion that abrupt changes in temperature and water vapour gradients in the atmosphere give rise to signal variations in good weather, while the absence of these discontinuities in bad weather allows of steadier signal conditions.