shot. No experimental data are available in the region of the calculation, but ball and crusher gauge measurements by the Naval Ordnance Laboratory ata ground point just beyond the region of these calculations appear to be in reasonable agreement with them. Very crude agreement with the theory was also afforded by the structural failure of the snap samplers on Greenhouse. These samplers had been designed according to the specifications in the theoretical study and, on Greenhouse Easy shot, successfully withstood the blast, whereas on Greenhouse George shot, where the reflected pressures were some ten times greater, the snap samplers were partially demolished. The values of pressure, density, and material velocity and their time variation in the region of regular reflection beneath the tower were calculated for a 50-kt bomb detonated on a 300-ft tower. Using a theory of strong shocks with variable gamma, all pertinent hydrodynamic variables in the incident wave at the ground were calculated from Operation Sandstonefireball measurements. The necessary equations of state were based on several sources and correlated by material later given in Thermodynamic Properties of Air.’ The corresponding peak values in the reflected wave were then calculated, using a treatment of regular reflection theory, which was reformulated to permit treatment of variable gamma. The calculated peak values for reflected pressure, density, and material velocity at the shock front furnished the boundary conditions at the front of the reflected wave for regions close to the ground. From these conditions, the mass flow behind the reflected shock was derived; the procedure is similar to the simpler problem of the freeair wave as in IBM Problem M,but using more rapid graphical and computational techniques. Pressure, density, and material velocity were necessarily carried forward during the integration, and temperatures were also deduced using the equation of state for high pressures in Ther- modynamic Properties of Air.’ Figures 1.2 to 1.5 are reproductions of Figs. 4.7 to 4.10 in WT-103, Greenhouse Handbook of Nuclear Explosions, and give the results of this calculation, as the time variation of pressure, density, material velocity, and temperatures, respectively, for various distances from Ground Zero. The curves for peak values are also shown. The early wave form is somewhatdif- ferent from that of a free-air burst, presumably because of the reflection process and the large entropy changes involved. These curves were prepared and should be regarded primarily as an exercise in strong shock hydrodynamics but probably constitute a reasonable estimate for 50 kt on a 300-ft tower. In general, the results cannot be scaled to different tonnages or different tower heights, except for rough orders of magnitude. Intuitively, one might expect the pressuredistance curve to be considerably flatter at angles within 45° of the bomb because the slant distance does not change greatly and because, at low pressures, the pressure multiplication does not vary greatly as a function of angle. This is not so in strong shocks for two reasons: First, the pressure multiplication falls off quite rapidly with increasing angle of incidence. This effect is then aggravated for the tower height and yield of Greenhouse Easy shot by the influence of variable gamma; as an example, y = 1.4 gives @ pressure multiplication of 8 at normal incidence, whereas for y = 1.2 the pressure multiplication is near 12 or 13 at normal incidence. Figures 1.3 and 1.4 contain the time variation of density and material velocity, respectively, and these are shown becausethey arethe parameters involved in the dynamic pressure. The density falls off ina manner similar to the manner in which peak pressurefalls off with distance. The material velocity, of course, is zero at Ground Zero, increasing rapidly to a maximum valueat the end of regular reflection. As a consequence, the dynamic pressure, '/ pu’, would follow a curve somewhat similar to the velocity vs distance curve, but this is not of primary importance becausethe flow is parallel to the ground. As such, the material velocity might contribute strongly to a scouring action by removing loose material near the edge of.the crater, and, if anything, would tend to fiftten the early crater rather than contribute to depth at the center. Figure 1.5 gives the tamperatures on the ground vs time and is of some further interest because the peak shock temperatures fall in the range 5000 to 9000°K. This is a range of tem- peratures which is favorable to the production of NO, and probably meansthat soil vaporiza- tion due to radiative transport is much less serious than one might supposeat first as a contributing mechanism for crater formation. The relative coolness of this layer and, in fact, the particular temperature range in which it falls, suggest that, if for no other reason, the ground surface will be protected from the radia-