more in the springtime. Figure 11 shows, in the broad view, a maximum in spring anda minimum in the autumn and is supported, more or less, for each year since 1955. The stratosphere is in phase with the deposition trends. Figure 12 shows further seasonal variations® at Milford Haven, England, but adds Ohakea, New Zealand, at 40°S. Note that the peak and valley in the Southern Hemisphere station occurs during its spring and fall also, but with only a small amplitude. The Southern Hemispherefall out is mainly that smal! fraction from the U. S. Pacific tests which mixed into the Southern Hemisphere stratosphere. In addition to differences in fallout due to large-scale air motions just described, there are also variations due to anomalies in precipitation amounts. There is a large body of evi- dence that indicates that the Sr® deposition is proportional to the amount of precipitation in a given area, Average annual precipitation plotted against cumulative deposition in soil up to about 1955 for selected sites! is shown in Fig. 13. The solid curve for stations in the eastern Mediterranean area shows most clearly the dependence of fallout on the amountof rainfall. The figure also shows that the greater precipitation in South America deposits less fallout, undoubtedly because the air concentration is lower. Fallout of Sr® in the United States in late 1956, as obtained from soil samples,’ is shown in Fig. 14. The higher fallout values in the northern tier of states, relative to the southern tier, has already received considerable publicity and is not new. Among the possible explanations are errors in the soil collection or analyses. Soil analyses apparently suffer from such serious difficulties that one is led to be suspicious of results that might not follow some reasonable pattern. But these data do reflect a pattern, with perhaps the exception of the 7 mc/ sq mile at Grand Junction. Further, from March through July 1956, the New York Operations Office of the AEC analyzed rain water from many Stations over the U. 8.43 The results also fell into a pattern (Fig. 15) for July 1956. It is clear that stations north of 40°N yield more Sr®™ fallout per unit of precipitation than stations to the south of 40°N. This puzzling difference in U. S. fallout is now a subject of research. 8 7 — 4 6 -— xc uJ be — 5 4 — G4 ~, a o” nn uw — 3a MILFORD HAVEN — 2-- 4 -- ee ¢ ~ mm Xe oeitLtitititti MAM & sJ 4955 SON DIS tt | OHAKEA em tit ~ymee x tt ppt FMAMJI 9 4956 AS ON te OILY pa FMAM J JA 4957 Fig. 12—~-Seasonal variation of Sr” content in rain water at Milford Haven, England, and Ohakea 322