approximation of a pressure-time curve could be obtained. Despite the fact that the cable to Station, 617.06, which was on a sandspit, broke soon after the air shock reached the gauge,it was possible to obtain readings of peak pressure and arrival time. Failure of the gauges and cables did not cause the carrier voltage (monitored during the entire recording period) at the other gauges to decrease, and the remaining gauges on both blast lines operated properly throughout the test. A possible source of error in the measurements made over water, for King shot, was the variation in the height of the tide. The elevations of the footings for someof the stations were above the mean low water spring tide (Table 3). The fact that the reef was exposed near the bases of someof the stations over water could conceivably have resulted in some distortion of the shock wave because of thermal effect, thus counteracting the advantage of the blast line over water. The height of the tide at the time of the shock wave on King shot was approximately 2 ft. However, the prevailing winds were in a direction such that they would tend to pile more water on top of the reef than would be indicated by the hydrographic charts. An exami- nation of Table 3 reveals that Station 617.06 was the only one whose base was completely out of the water; others may have been awash. Results obtained from the measurements do not give evidence of any sezious distortion of the shock wave, probably because at least 95 per cent of the reef on which the measuring stations were installed was awash or under water and because the hard rock of the reef was not overly subject to the type of superficial thermal explosion usually associated with distortions of this type. An inherent and undesirable characteristic of the Ampex recording system as used for these tests was the tendency toward zero drift in the playback of the record. It was necessary to use a considerable amount of arbitrary judgment in establishing a base line for records from all gauges on both Mike and King shots, with the result that data on the negative phase — peak pressures, durations, and impulses —are subject to a potential error of significant magnitude. 5.2 Analysis of Results (a) Mike Shot. Data from the air-pressure measurements on Mike shot are presented in Table 4. The arrival time at Station 615.02 was obtained from the low-range gauge connected to the Baker recorder on Bogon. It might also be noted that, since the arrival time on the USS Estes was determined by means of a stop watch, it is accurate only to within 1 sec (1 per cent). From Table 4 and from the pressure profiles (Figs. 8 and 9) it can be seen that there is a sizable discrepancy between the peak pressures measured by the gaugein the side-onbaffle and by that in the pitot static tube at Station 611.01; a similar discrepancy was observed between the readings for gauges of the same type at Station 612.01. The difference at Station 611.01 cannot be attributed simply to statistical variation;* it is possible that the lower reading from the gauge in the side-on baffle could have resulted from a leakage path across the terminals, caused by excessive moisture. Although the calibration steps for each gauge would have revealed any changes in system amplification, it would have been impossible to detect a leakage path in this manner. Too, evidence from wind and temperature measurements’® leads to the belief that the higher reading of peak overpressure (20.5 psi) is the morereliable. Each of these measurements—total head, dynamic pressure, and temperature —gave results consistent with those expected from a peak overpressure of 20 psi. The difference be- tween pressures measured at Station 612.01 may be within the limit of statistical deviation, for, although the difference is comparatively great, the pressures being measured were rather *The term “statistical variation” takes into account the accuracies of the system andin- strumentation and is a means for expressing the differences in signal level observed when identical pulses act upon identical gauges. 23