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Over a four year period, from September 1967 to July 1971, the rate of growth of a 30 micron radius drop to 50 or 100 micron radius by a process known as accretion has been studied as part of the numerical modeling effort of Project Themis. A mathematical model was derived which considers a single 30 micron radius drop falling at its terminal velocity through a field of smaller, 5 to 20 micron radius droplets, and growing by colliding and coalescing with droplets in its path. The droplets also fall at their terminal velocities and the rate of growth of the drop is proportional to the difference in the terminal velocities of the colliding drop and droplet as well as the area of sweep of the falling drop and the number of collectible droplets per unit volume of cloud. Hydrodynamic and electrostatic forces influence the rate ofgrowth and are accounted for by introduction of a 'collision efficiency' term to the analysis. Electrical forces also influence the terminal settling velocities of the particles, so Stoke's law of drag on a sphere and the intermediate law were derived incorporating these forces., Report on Themis Sub-Project on Mathematical Modeling of Cloud Growth.

As part of a study to develop means of estimating the ability of soils to permit vehicular traffic, a method was developed for predicting the moisture content of soils. Data used in development of the method were obtained from daily soil moisture and weather records kept for periods of one to two years at 131 sites throughout the United States. Chief influences on moisture accretion in the surface foot of soil were found to be the amount of rainfall and the amount of space available in the soil for water storage. Moisture depletion rates varied with the moisture content of the soil but followed characteristic curves for each season. The prediction method was tested on more than 600 sites throughout the United States.

Microchemical analysis and x-ray micrographs were performed on thin slices of ice cylinders artificially grown in a tunnel by accretion of supercooled droplets of contaminated water. Characteristic distribution patterns of contaminants were determined for various types of growth, with reference to contaminant transport that can take place in bulk ice. The results, if extended to natural hail, can be very helpful in inferring the environmental growth conditions. (Author)

Bottom changes occurring in Monterey Harbor from 1932-1969 were analyzed by numerical computer methods using 15 selected hydrographic surveys. Results of the study indicate that the major portion of the harbor has been shoaling in the mean since 1932. The long-term shoaling rate has been 0.4 to 4.0 feet per decade in the beach and nearshore zones and along the breakwater; and less than 0.25 feet per decade in the stable outer harbor. The accretion rate averaged 17,500 cubic yards per year from 1932-1969, but only 7,100 cubic yards per year from 1947 to 1969. The shoaling is believed due to the construction of the Coast Guard Breakwater in 1931-1934. It is deducted that prior to 1960 the excess sand was carried into the harbor by littoral transport from Del Monte Beach and by wave currents around the breakwater. Construction of the solid wall on Wharf 2 in 1960 cut off the former sand supply. Local redistrubution of sand in the beach and nearshore zones of the harbor is large and results in areas of significant accretion and erosion between surveys. Dredging operations have had only short-term effectiveness because the spoil has been retained within the harbor. (Author)

A theory of the origin of the solar system is discussed, including introduction and general principles, accretion of planets, partial corotation of a magnetized plasma, and the structure of the Saturnian rings. (Author)