208 
TABLE 3—Comparison of computed distributions 
and observed values for Stratus, number of drops 
per cms 
Observed (Stratus B) 
Size range r 
Case | Case | Case | 3000 | 6000 
1 2 3 sec sec 
micron 
1.5-2.9 14} 66; 47} 35) 40 
3.0-4.3 70 | 120 | 142 25 20 
4.4-5.7 66} 60 | 210 | 230} 10 
5.8-7.0 17 17 | 59] 90 5 
7.1-8.1 12 9 18 9 5 
8.2-9.1 6 2 7 1 5 
9.2-10.5 3 0 0 0 5 
10.6-11.7 1 6 3 205 
11.8-12.8 1 2 7 90 
12.9-14.1 1 2 3 28 
14.2-15.0 0 0 0 1 
15.1-16.0 0 2 0 il 
i 
lar to ours. In his cases also the nuclei smaller 
than one-tenth micron did not grow while the 
larger ones did. This shows that the general nature 
of the results is not sensitive to the initial con- 
ditions, nor even to the error he made in the ap- 
plication of Raoult’s law. 
It is planned to undertake computations of the 
growth of drops by the combined effects of con- 
densation and coalescence, and subsequently to 
take account of the three-phase process as well. 
For this purpose accurate collection and coales- 
cence efficiency data are needed. At present the 
uncertainty, particularly with respect to the 
efficiency of collection of nearly equal sized small 
drops, would leave the validity of the results 
of such computations considerably in doubt. 
Nevertheless the computations may give a con- 
siderable insight into the precipitation process. 
Simplified computations have already contributed 
to the clarification of the problem (Houghton, 
1950; East, 1957]. The computations using the 
electronic digital computer should provide further 
enlightenment. 
Acknowledgments—The computations were car- 
ried out on SWAC, the electronic digital com- 
puter operated under a contract with the U. 8. 
Navy Office of Naval Research by the Numerical 
Analysis Research Group of the Department of 
Mathematics, University of California, Los Ange- 
les. Time on the machine was provided without 
charge, and our gratitude to the Numerical Anal- 
ysis Research Group and the Office of Naval Re- 
search is hereby acknowledged. We wish to thank 
the staff of the Numerical Analysis Research 
NEIBURGER AND CHIEN 
Group also for suggestions and assistance in pre- 
paring the problem for the computer. 
REFERENCES 
Auty, T., ano C. A. Mackay, The accommodation 
coefficient and the evaporation coefficient of wa- 
ter, Proc. R. Soc. London, A149, 104-116, 1935. 
ANDERSON, C. E., Diffusion growth problem in 
cloud physics, Artificial stimulation of rain, 
Pergamon Press, pp. 153-160, 1957. 
Barrer, E. O., anp L. 8. Germain, Growth of 
drops formed in a Wilson cloud chamber, Rev. 
Sci. Instr., 18, 84-86, 1947. 
Best, A. C., The size of cloud droplets in layer- 
type cloud, Q. J. R. Met. Soc., 77, 241-248, 1951. 
Byers, H. R., anp R. R. Branam, The Thunder- 
storm, Report of Thunderstorm Project, U. 8. 
Government Printing Office, Washington, D. C., 
1949. 
CHAPMAN,S., AND T. G. Cow1ina, The mathemati- 
cal theory of non-uniform gases, Cambridge Univ. 
Press, Cambridge, 1952. 
Diem, M., Messungen der Grésse von Wolkenele- 
menten, II, Wet. Rundschau, 1, 261-273, 1948. 
East, T. W. R., An inherent precipitation mecha- 
nism in Cumulus cloud, Q. J. R. Met. Soc., 83, 
61-76, 1957. 
Evpripar, R. G., Measurements of cloud drop-size 
distributions. J. Met., 14, 55-59, 1957. 
Friscu, H. L., anp F. C. Coutirns, Diffusion proc- 
ess in the growth of aerosol particles, J. Chem. 
Phys., 20, 1797-1808, 1952. 
GILBERT, J. Y., Condensation nuclei of the Los An- 
geles region, Research Rep., Dept. of Met., 
Univ. Calif., Los Angeles, 1954. 
Houcuton, H. G., Evaporation of small drops, 
Physics, 4, 419-424, 1933. 
Hovuaurton, H. G., Preliminary quantitative anal- 
ysis of precipitation mechanisms, J. Met., 7, 
363-369, 1950. 
Howe t, W. E., The growth of cloud drops in uni- 
formly cooled air, J. Met., 6, 134-149, 1949. 
Junag, C. E., Gesetzmissigkeiten in der Gréssen- 
verteilung atmosphirischer Aerosole tiber dem 
Kontinent, Ber. Disch. Wetterdienst U.S. Zone, 
35, 261-277, 1952. 
Junas, C. E., Die Rolle der Aerosole und der gas- 
formigen Beimengungen der Luft im Spuren- 
stoffhaushalt der Troposphire, Tellus, 5, 1-26, 
1953. 
LanemurrR, I., Super-cooled water droplets in ris- 
ing currents of cold saturated air, Rep. RL-223, 
General Electric Research Laboratory, 1944. 
Lopaer, J. P., A study of sea-salt particles over 
Puerto Rico, J. Met., 12, 498-499, 1955. 
Ma xus, J. 8., Some results of a trade-Cumulus 
cloud investigation, J. Met., 11, 220-237, 1954. 
Mason, B. J., The Physics of Clouds, Oxford Univ. 
Press, London, 1957. 
McDonatp, J. E., Erroneous cloud physies appli- 
eation of Raoult’s law, J. Met., 10, 68-70, 1953. 
Morpy, W. A., AND L. E. Esper, Observations of 
rainfall from warm clouds, Q. J. R. Met. Soc., 
80, 48-57, 1954. 
