those on Tumbler shots | to 4 in that there was little or no decrease in positive impulse deSpite a sizable attenuation of peak pressures. On Tumbier shots 1 to 4 it was found that the decrease in positive impulse (10 per cent) was considerablyless than would have been expected as a result of the decrease in peak pressure. To augment the data compiled on surface bursts of atomic weapons, it would be highly desirable to instrument a surface burst of operational size over land so that the blast line is en- tirely over land. If no continental test site were available for a surface burst of this size, it could be performed at Eniwetok on Engebi. Increased interest in contact fuzing is a strong argumentin favor of a burst of this type. Measurements of the type made on Mike shot should be repeated at the earliest opportunity on a detonation of a superbombto test the validity of the assumption that a surface burst has the same effectiveness as a bomb of twice the yield burst in free air. It would not be necessary to extend the blast line to the low-pressure regions instrumented on Mike shot except as indicated to explore the effect of atmospheric nonhomogeneities. It is desirable, however, to measure overpressures from the higher-overpressure regions (100 psi) to those overlapping the higher pressure levels instrumented on Operation Ivy. Measurements of this sort are currently planned for Operation Castle. REFERENCES 1 B. F. Murphey, Air Shock Pressure-Time vs Distance, Tumbler-Snapper Report, WT-501, August 1952. 2. C. J. Aronson et al., Free-Air and Ground-Level Pressure Measurements, Tumbler- Snapper Report, WT-513, November 1952. . B. F. Murphey, Air Overpressure vs Time vs Distance from Buster Airburst Bombs, Buster-Jangle Report, WT-304, March 1952. . W. J. Howard and R. D. Jones, Free Air Pressure Measurements for Operation Jangle by Project 1.4, Sandia Corporation Report SC-2261(Tr), February 1952; also issued as WT306, Air Pressure vs Time, and as an integral part of WT-367, Blast and Shock Measurements IZ. . J. M. Harding, Variations of Blast Pressure at Fixed Distances with Small Altitudes, Buster-Jangle Report, WT-305, April 1952. . G. K. Hartmann et al., Blast Measurements, Greenhouse Report, Annex 1.6, Part I, WT- 64, May 1952. . G. K. Hartmann et al., Pressure-Time Measurements for Operation Sandstone, Sandstone Report, Annex 5, Vol. 22, Part III, June 1948. . Report of the Technical Director, Operation Crossroads, Vol. I, Report XR-156, May 1947. F. Reines and B. R. Suydam, Preliminary Survey of Physical Effects Produced by a Super Bomb, Los Alamos Scientific Laboratory Report LAMS-993, November 1949. 10. M. Peter et al., The Effects of Large Yield Atomic Bombs, RAND Corporation Report RM-866, July 1952. 11. F. H. Shelton, The Precursor, Sandia Corporation Report SC-2850(Tr) (in preparation); F. Porzel, Height of Burst for Atomic Bombs, Los Alamos Scientific Laboratory Report LA- 1406 (in preparation). 12. E. J. Zadina, LASL Memorandum fo W. E. Ogle, LASL, Effects of a Super Detonation at Eniwetok Atoll, Ref. sym. J-9122, Dec. 3, 1951. 13. E. J. Zadina, LASL Memorandum to R. H. Campbell, LASL, Pressure-Distance Curve for 500 Kilotons, Ref. sym. J-9220, Dec. 12, 1951. 14, R. S. Millican and H. E. Lenander, Sandia Laboratory Operational Report on Operation Ivy, Program 6, Ivy Report, WT-606 (in preparation). 15. J. D. Shreve, Jr., Pressure-Distance-Height Study of 250-1b Spheres (App. B), Tumbler Report, WT-520, March 1953. 62