PREFACE 



vu 



by Miss Jean Smith and Mrs. Frances Schaefer, who typed the greater part 

 of the manuscript, and by Ellis H. Myers, who assisted in preparing the 

 diagrams and graphs. We are especially grateful to Miss M. J. Brandenburg, 

 who not only typed a large part of the manuscript, but also read the entire 

 manuscript and proof, offering many important suggestions and corrections. 

 Many others have been very helpful in the preparation of the manuscript. 

 Among these we wish especially to express our sincere thanks to Drs. R. R. 

 Newell, B. J. Moyer, A. C. Helmholz, and H. B. Jones for critically reading 

 parts of the manuscript and making many corrections and suggestions. 



William E. Siri 



Berkeley, Calif. 

 June, 1949 



