Table 4— RATIO OF Cs8? ro sr** DEPOSITED IN VARIOUS PARTS OF THE WORLD 1955 Station Kinloss Liverpool Snowdon Abingdon Milford Haven Felixstowe 3 1956 4 1 2 3 4 1 1.29 1.92 1.76 2.93 1.56 0.69 1.68 1.45 1.71 2.36 1.63 1.03 2.47 0.89 1.63 1.40 0.86 1.79 1.45 2.64 1.68 1.24 1.25 2.32 1.25 1.58 1.68 1.24 0.78 0.40 0.45 0.47 0.51 1.25 2.45 2.51 0.29 1.89 1.26 1.76 4.87 0.60 3.50 2.22 1.20 1.20 2.10 0.35 1.27 1.66 ~1.66 ~2.01 0.49 1,99 171 1.44 1.22 Ottawa 1.96 1.79 Gibraltar Port Harcourt Singapore Suva Melbourne Ohakea Port Stanley 1957 1.00 2.16 2.17 1.52 0.64 1.62 3.50 0.46 1.47 1.40 2.48 2.00 0.32 0.60 1.56 1.47 2 Mean value* 1,66 sited * Mean value = Total Ca'? depo Total Sr°” deposited total Cs'*" to total Sr®® deposited at each site. It is clear that there is a considerable scatter in the values of the ratio. The statistical errors involved in counting the Sr® and Cs!*" are only of the order of 1 or 2%; all the errors involved in the chemical processing and source preparation have been estimated to be about +5% but even allowing an error of +10%, the ratios of the two isotopes would be expected to be distributed with an error of +15%. The mean of all the values obtained is 1.50 as expected but it is obvious that consistently low values, well outside the statistical margin of error, are obtained at Gibraltar and Melbourne, with fairly high values at Liverpool. No satisfactory meteorological explanation is as yet forthcoming for this phenomenon. The possibility cannot be ignored that the phenomenonis not a true one but is a feature of the sampling system. This is thought to be unlikely, as the procedure is exactly the same at all stations, but the polythene collecting bottles at several stations, including Gibraltar and Liverpool, are being returned to the laboratory to be examined radiochemically for evidence of adsorption of Cs'™in particular. The excellent agreement between the Sr°° collected at Milford Haven in the two independent systems with and without carrier has already been noted. It is noticeable, however, that the mean Cs'*/Sr®® ratio obtained on the carrier- free quarterly collecting system at Milford Haven is about 16% less than that derived from the monthly system where carrier is always present. In addition to the check on the collecting system, an experiment is currently being carried out at Gibraltar in which the Cs'*"/Sr®® ratios in rain water samples are being compared with the ratios obtained from dust samples collected from the air in the troposphere above Gibraltar. 8 Sr*? AND THE GENERAL CIRCULATION OF THE ATMOSPHERE The programme of measurements has revealed certain general facts about the Sr* in the atmosphere, in rain water and on the surface of the earth: (1) Since 1954, nearly all the sr*? deposited at places remote from test sites has been de- rived from large-scale nuclear explosions and has been fed down gradually from the stratosphere. (2} The concentration of Sr*° in rain water, and hence in tropospheric air, shows a genuine seasonal variation, having opposite phases in the two hemispheres. There is a strong indication, in the northern hemisphere at least, that this variation is in step with a similar variation in the lower stratosphere. (3) The greatest deposition takes place in the middle latitudes. (4) Deposition in the northern hemisphere is greater than that in the southern hemisphere 242 Sto