vill PREFACE 
Our gratitude is also due to Dr. H. Landsberg, then President of the Section of 
Meteorology, American Geophysical Union, Dr. Alan Waterman, Director, National 
Science Foundation, and Dr. Earl Droessler, Director, Atmospheric Sciences Pro- 
gram, National Science Foundation, for their support in making this Conference 
possible. Finally, we like to express our thanks to Mr. Waldo E. Smith, Executive 
Secretary, American Geophysical Union, for his untiring suport and efficient help 
in all phases of the Conference from the initial planning to the final editing phase. 
A word should be said with regard to the form of this publication. The practice 
of publishing the complete proceedings of a conference in book form is becoming in- 
creasingly popular in recent years, but 1s nevertheless also subject to criticism. It is 
pointed out that the papers could be published in current journals and that the dis- 
cussions quite often and of necessity contain thoughts or ideas that are not always 
well ripened. In spite of this we considered this publication a worth-while under- 
taking mainly for two reasons: (1) The publication of the papers in one volume will 
convey to the reader not only much of the present state of the art of precipitation 
physics, but also of the special scope of this Conference, namely, the significance of 
this field within the larger scales of atmospheric flow patterns. (2) Many of the dis- 
cussion remarks greatly contributed to this aim and form therefore important links 
between the sessions, therefore, much of the stimulus for further research would be 
lost through their omission. This is particularly true of the very interesting discus- 
sions related to the last session on Artificial Precipitation Control. 
It is therefore hoped that this volume conveys to the reader something of the 
stimulating atmosphere of this Conference which in the consensus of the participants 
was a full suecess. Professor Bergeron, the Honorary Chairman, called it in his clos- 
ing remarks one of the best meteorological conferences which he had ever attended 
throughout his 40 years of professional work. The merits for this success are his own 
in view of his stimulating papers and his inspiring discussion remarks, and those of 
the authors for their interesting papers, of the chairmen for their able direction of the 
sessions (always being under pressure of time), of the participants for their stimulat- 
ing discussions and endurance (one discussion period lasted until midnight), and 
last, but not least, of all who took part in arranging and setting up facilities and 
schedules. 
On the background of this cooperative effort, the goal of the Conference was 
achieved in a way which surpassed our expectations. Justice was not only done, in 
the lectures, to the various scales of precipitation physics, as outlined above, but 
justice was also done to the next higher level of information, namely, to show how 
tightly interwoven these scales can be with one another. What we mean is illumi- 
nated in the contributions which showed the close relationship between the size dis- 
tribution and concentration of nuclei and the size distribution and concentration of 
the cloud droplets (W. A. Mordy, M. Neiburger and C. W. Chien, P. Squires and 
S. Twomey); and between the latter and the size distribution and concentration of 
‘aindrops precipitated from these clouds (P. Squires and 8. Twomey). Thus for cer- 
tain types of rain, no link is missing in the chain which connects the microscale with 
the mesoscale. 
Another example from the papers which lead from the study of snow crystals to 
the fine structure of precipitation processes (U. Nakaya and Ix. Higuchi, J. Grunow, 
Ch. Magono), or from a microscopic study of the hailstone structure to an under- 
standing of its life history within the hailstorm, and thus, ultimately, to an under- 
standing of the hail mechanism (R. List, R. Sanger). These research projects open 
