Data on the crystal structures of the common modifications of the elements at zero pressure.

This technical report is intended as a brief description of the free convection problem existing in the various annuli of the SIR Mark A rotating plugs. It is by no means a complete report of the plug "hot tests", but merely records some of the more significant experimental observations and presents a few of the theories and calculations made to explain the observed free convection phenomenon. The general discussion which follows is chronological. Details of analyses are relegated to the Appendix.

Formulas derived from earlier work satisfactorily predicted low frequency ground effects resulting from the Pre-Gnome explosions, but they not predict high accelerations associated with high frequency ground waves. The Pre-Gnome experiments taken since indicated that accelerations and ground amplitudes are proportional to the explosive charge, but physical conditions limit extrapolation on this basis to relatively low yields. Predicted accelerations resulting from the 10 kt Gnome explosion in potash mines eight or more miles away will be somewhat less than from routine blasts in the mines. The compressional wave speed in the salt stratum of the area is about 14,000 feet per second.