since the actual temperatures in the fireball interior can only be surmised; the surface is certainly much cooler, and we can observe only the surface. The published data may be found in the literature.¢»3,4,> These data are summarized in the curves given in Figure 1. Although there is some scatter to the data, it is clear that gamma goes through a broad minimum, and is of the order 1.2. | Thus Taylor's theoretical scaling constant K = 1.740 differs from the experimental value K = 1.709 by only 2 percent, and we use the experimental number in evaluating all USAEC test shots. The energetic equation is, then, E = 1.709p R°t~* (ergs) . (2) In practice the USAEC has measured the fireball diameter, rather than the radius, and has used a different set of units throughout, Expressing Din meters, t in milliseconds, p, in grams/liter, and E in kilotons, relation (2) may be rewritten: 5 E = 1.272 x 1078pD°t™ kilotons (3) where we use the conversion factor, one kiloton = 4.2 x 1019 ergs. This conversion factor, although somewhat arbitrary, has been used consistently. os. G. Logan and C. E, Treanor, Tables of Thermodynamic Properties of Air from 3,000°to 10,000°K, Cornell Aeronautical Lab Report BE-1007-A3, January 1957. 3 J.O. Hirschfelder and C. F. Curtiss, Thermodynamic Properties of Air, II, Naval Research Lab Report CM-472, University of Wisconsin, June 1948. 43, Hilsenrath and C. W. Beckett, Tables of Thermodynamic Properties of Argon-Free Air to 15,000°K, Arnold Engineering Development Center Report AEDC-TN-56-12 (ASTIA AD-98974). ° Thermodynamic Properties of Highly lonized Air, AFSWC-TR-56-35 (ASTIA AD-96303), Kirtland Air Force Base, New Mexico. 6