1082 evident on the pressure-time curve; Sendia'’s tine of arrival refers of course ALi to the pressure :.. in the “thermal shock . Wigore 2 shows the peck pressure vs. distances over land and vater. Here again the agreassnt with the theoretical predictions is conatéered ex- cellent, both over land and water. Hote the return of tho thermal curve | to approach the ideal values near 8 yeti. Purther, veyond 10,000 foet the pressures are below ideal, indicating that the effect of ataoepheria inhom- gmneity sets in somewhere beyond 19,000 to 15,000 feet. Figur: 3 shows the positive duration vs. bcrisontal distances. ‘The theoretical curves ara not exact; for simplicity, I have used here the posi- tive duration of « free air curve with @ reflection factor of 2. For a dca at altitude, the cloencia positive duration should de more nearly like 1/2 the tonaage indicated here. On thecurves, the two close-in ideal surface positive durations are, in fact, shorter than inéicated but at large dis- tances for the positive durations become much longer then predicted. This is attributed to atucupherie inhcuogeneity setting in beyond 15,000 feet. Hote also that the ponitive durations are considerably longer over lanl than ovar water; this is again due to thermal effect andi precursor action, with aoe reinforcenmt of the dDlast wave from thermal vadiatics. BEST COPY AVAILABLE 3. MIKE chor During bis visit last week, Lew Fussell reported thet the mora recent fireball measurements are giving values of / like 268 from the Perry-Dastmn filme, and 278 from the Engeht Rapntronics. ‘The fireball measurenents at Ferry, which resulted in the firevell yield of 12 megatons, was based on data whose / values vere more like 2773 now the Ingebl messuremengs will be large decause the apparent wise of the fireball is measured by the tangent to the fireball, end at theese close-in distances, the proper correction will reduce Wa geab roELT ree at eB” :