Acknowledgements 
The author again wishes to express his sincere thanks to 
the many people who have helped in the preparation of this work. 
The continued help, cooperation, and interest of all of the 
people and of the organizations mentioned in Part One is deeply 
appreciated. The interest with which Part One has been received 
is gratefully acknowledged. 
Thanks are also due to Mr. Dean F. Bumpus for the aerial 
photographs used in Chapter 12. They illustrate many important 
properties of wave refraction. 
July 1, 1952 Willard J. Pierson, Jr. 
Department of Meteorology 
New York University 
Ted: 
