408 KALKSTEIN, THOMASIAN, AND NIKULA with the principal disturbances occurring late in the winter.® This also is reflected in the measurements of the concentrations of !°°Cd, with the high-latitude increase in the northern hemisphere first beginning about December or January and reaching high levels in March and April of 1964, In addition, the northern-hemisphere concentrations have been consistently lower than those in the southern hemisphere. The latest stratospheric concentrations presented here correspond roughly to one-half of what was expected on the basis of the ‘Rh experiment. This could be due to less than average transport of the !°°Cd tracer to the low stratosphere, escape of some of the tracer from the earth’s magnetic and gravitational field, or a lower production of the 108°Cd than 0.25 Mc. The last possibility would be consistent with the value of about 0.12 Mc estimated by Cowan.” REFERENCES 1, U.S, Atomic Energy Commission Health and Safety Laboratory Cadmium-109 Conference, Dec. 6, 1963. (A ““best’’ estimate of 0.25 + 0.15 Mc of Cd!was arbitrarily adopted.) 2. I, J. Russell and R.V, Griffith, The Production of Cd!® and Cd!!3™ in a Space Nuclear Explosion, in Fallout Program Quarterly Summary Report, USAEC Report HASL-142, pp. 306-322, Health and Safety Laboratory, Jan. 1, 1964. 3, M,I. Kalkstein, Rhodium-102 High Altitude Tracer Experiment, Science, 137: 645 (1962), 4, L, P, Salter, in U. S, Atomic Energy Commission Health and Safety Laboratory Cadmium-109 Conference, Dec. 6, 1963. 5, H. Wexler, Seasonal and Other Temperature Changes in the Antarctic Atmosphere, Quart. J. Roy. Meteorol. Soc., 85: 196 (1959). 6. W. S. Hering, Air Force Cambridge Research Laboratories, private communication, July 1964, 7, G, A, Cowan, memorandum to the U, S, Atomic Energy Commission Health and Safety Laboratory Cadmium-109 Conference, Dec. 6, 1963.