-5detailed plot of cumulative $r9 fallout vs. time at our Pittsburgh “washtub"” station. The meteorological reasons for the variations in slope are still only slightly understood. The Public Health Service program (Table I) provides rapid notification and documentation of the arrival and presence of fresh test debris in air and rain. The main use of the data is thus qualitative, but they also would indicate when gross levels of radioactivity are sufficiently high to warrant more detailed investigation. The program of the Air Force Cambridge Research Center, recently begun and partially supported by the AEC, provides large-area rain samples for detailed analysis at selected stations of the Naval Research Laboratory air filter network. The Air Force Cambridge Research Center and the Weather Bureau are also collecting samples for tritium (H3) analysis. Soil samples, properly selected, provide the best measure of the total Sr-90 which has fallen per unit area of earth’s surface. The analysis of bulky samples of soil for the minute traces of Sr-90 is far more difficult than the analysis of the more concentrated types of samples. The collecting and retaining properties of soils together with their flora and fauna are not well known and may be highly variable. It has been possible by extremely careful and laborious methods of soil sampling and analysis to obtain reliable measurements of total fallout representative of many land areas of the earth (Fig. 5) and to obtain useful estimates of increments over intervals of about 1 to 2 years. Plotted against latitude (Fig. ®) » the 1956 dataclearlyfives the northern hemisphere middle latitude maximumof sr90 fallout. soils, still in process of analysis, reaffirm this pattern. The 1958