rhodium. Since there was about 0.3 Mc of Rh 10 . . 4: 2 produced in other tests of the Hardtack series, the possibility that some of the early rn? is due to sources other than Orange cannot be entirely ruled out. In any case, the conclusion of slow mixing between hemispheres seems valid, From Figures 4 and 5, it can be seen that there is considerable variation of concentration with latitude. The most obvious features of this distribution pattern are the relatively uniform and equal high concentrations at high latitudes in both hemispheres with a rather sharp drop to low concentrations at the low latitudes. It would indicate that there is a large difference in the mixing pattern in the two regions (high latitude and low latitude). This is to be expected on the basis of meteorological evidence, References 1. G. W. Johnson, UCRL-6030-T, Application of Nuclear Explosions as Seismic Sources. 2, M. I. Kalkstein, BAPS Series II, Vol. 6, 229 (1961). Later results subsequent to this reference indicate that the half-life for the long-lived isomer of Rh!192 is roughly four years rather than 2.5 years, 3, F. K. Hare, J. of Meteorology 17, 36 (1960). 75-76