low. Also, the gauge used in the pitot static tube was a 10-psi (full-scale) gauge rather than a i1-psi gauge, as should have been used at this station. The 10-psi gauge had an absolute error of about 0.1 psi in addition to the system error of approximately 5 per cent. Kiel gauge meas- urements at this sameatation’® gave the total head as approximately 0.51 psi. At this pressure the dynamic pressure is so low that the total head is almost the sameas the static pressure. The pressure-time profiles for the various stations (Figs. 8 and 9) are not unusual except that at large distances and low pressures there is a rounding off of the peaks. The tabulated data from Mike shot are presented graphically in Figs. 10 to 16. In the curve of arrival time vs distance (Fig. 10), only a single data point is plotted for each station, since arrival times at the two gauges were almostidentical. In the curves showing variation of peak positive pressure, positive-phase duration, positive impulse, peak negative pressure, negative-phase duration, and negative impulse with horizontal distance from ground zero, the values for each gauge are plotted, using appropriate identifying symbols. No attempt was made to draw the curves through every point; the curves were fitted visually and merely give a general indication of how the function in question varied with horizontal distance from ground zero. (o) King Shot. Data from the air-pressure measurements on King shot are presented in Table 5. Absence of data on the negative phase from Stations 617.03 and 6101.01 is a result of inability to make the correction for tape wow. As will be seen from a comparison of Tables 2 and 5, distances of the various stations from ground zero differed considerably from those intended; by the same token the distances from ground zero to the corresponding stations over land and water were quite different. Consequently, in constructing pressure-time profiles (Figs. 17 to 19) for the corresponding stations on the land and water lines (6101.01-617.02, 6101.02-617.04, 6101.03-617.06, and 6101.04617.07), it was necessary to correct arrival times at the stations over water for comparison + . with those at the land-line stations. The only really serious discrepancy was between Stations 617.07 and 6101.04, for which the intended distances from ground zero had not been the same. The pronounced dips in the pressure-time profiles for the gauges at Stations 617.03 and 617.04 are attributed to rotation of the gauges. There was a strong temptation to draw a smooth curve from the peak to the crossover point, but it was thought preferable to show the actual shape of the curve. A comparison of the profiles for the gauges over water with those for the land-line gauges emphasizes the fact that the blast wave traveling over water exhibited a sharp rise time and a well-defined peak, decaying smoothly to zero; in fact, it was almost a perfect “textbook” wave- & form. That traveling over land, on the other hand, was obviously affected by thermal radiation. *Only the first station on the land line (6101.01) actually recorded any definite evidence of a precursor; if there was a precursor at the second station (6101.02), its magnitude was such that it was all but indistinguishable from the background noise. The main shock wave appeared to have a slow rise time and a peculiar double peak. At two stations farther out along the blast line there was definite evidence of recovery from the thermal effect, i.e., a sharp rise to with- in 80 to 90 per cent of the peak pressure and a rounding off of the peak. An interesting phenomenon observable from the data on King shot was the second shockat the very beginning of the negative phase (Figs. 17 to 19). Data on this second shock are presented in Table 6; the peak overpressures tabulated are the actual rises measured, consider- ing the pressure at the time of arrival of the second shock as ambient. It is unlikely that this shock couldbe attributable to a shocking up of the negative phase, since such a shock would occur at the end rather than at the beginning of the negative phase. Such a second shock has been noted before,'.? but at the end of the positive phase or nearer the crossoverpoint. Although no second shock was seen by the gauges as far from ground zero as those on Parry,it is probable that its magnitude at this distance would have been such (~0.03 psi) that it would have been lost in the background noise. Positive-phase durations (Table 5) for stations on the land line were taken from the point at which the pressurefirst beganto rise to the crossover point; no attempt was made to com(Text continues on page 39.) 28 Se