Preface 
The Second Woods Hole Conference on Cloud Physics, June 3-5, 1959, was de- 
voted to the subject Physics of Precipitation. This volume contains the papers which 
were presented during the sessions as well as the edited discussion remarks. 
Two antagonistic requirements exist which make a planning of a conference very 
difficult: (1) one has to be able to discuss the details of the subject matter and (2) 
one would like to understand the matter in a larger frame and in its general signifi- 
cance. In modern science and perhaps especially in cloud physics the details of the 
subject branch out widely into other fields in which the seale and movements of 
atoms and molecules form the principal size parameters, whereas the larger frame of 
cloud physics, which is mainly connected to meteorology, of necessity ends in pat- 
terns determined by the scale and movements of the world-wide atmospheric circu- 
lation. In the past the large-scale and macrophysical aspects of cloud physics had 
often been neglected on account of the emphasis which was put on microphysical 
processes of clouds, and in clouds and cloud particles. In the planning of this Con- 
ference, an effort was therefore made to do justice to macrophysies and to reconcile 
this range of 10'° orders of magnitude by illuminating the subject matter from three 
different vantage points: (1) from the scale of synoptic meteorology, (2) from the 
scale of clouds and cloud systems, and (3) from the scale of microphysics. In agree- 
ment with this planning three main sessions evolved: A/orphology of Precipitation 
Clouds and Cloud Systems, Morphology of Precipitation and Precipitation Particles, 
and Fundamental Precipitation Processes. 
It was then considered that, with the ground thus prepared, a fruitful discussion 
of the problems connected with Artificial Precipitation Control will evolve which 
would give a fourth session. 
The letter of invitation sent to the participants outlined this plan. After the pro- 
posed papers had been received, it turned out that a special session on Hail Forma- 
tion could easily be formed. 
The location chosen for the meeting was again the Woods Hole Oceanographic 
Institution. This was done in order to emphasize the significance of cloud processes 
at the water-air interface for the supply of water vapor in the planetary circulation. 
These processes are one of the objectives of the research work of that Institution 
which has brought about a series of significant studies on microphysical as well as 
macrophysical processes connected with the formation of clouds or precipitation. 
The fine hospitality received from this Institution is gratefully acknowledged. 
With the stage thus set for an interesting conference, it was exceedingly fortunate 
to have not only many of the cloud-physics experts of the United States but also a 
number of the foremost scientists from abroad participating. There is, of course, one 
scientist who is most intimately connected to the subject matter since he is not only 
one of its founding fathers but also one who is able to speak with authority on all 
three scales involved: Professor Dr. Tor Bergeron. It was therefore a privilege that 
he agreed to serve as Honorary Chairman of the Conference. We are glad to express 
our sincere gratitude for his most inspiring and stimulating participation. 
We also want especially to mention and express thanks to Dr. G. Wolff and Prof. 
Dr. A. Goetz for their participation. These scientists are not immediately connected 
with the subject matter, but serve as consulting experts, the former in crystal phys- 
ics and the latter in physical chemistry. Prof. Goetz was also representative of the 
American Physical Society. . 
vii 
