PREFACE 



The announcement of the microscopic appHcation of the pT 

 trast method by Professor F. Zernike in 1935 marked the beginning of 

 new and outstanding progress in the field of microscopy. The phase 

 contrast procedure has made possible the microscopy of an important 

 class of materials that could not be satisfactorily examined with previ- 

 ously existing microscopic methods. In the early stages of the wide- 

 spread, international development of the phase technic the authors of 

 this book began their investigations which resulted in significant con- 

 tributions to the theory, instrumentation, and application of this highly 

 effective procedure. Concurrently and independently, scientific workers 

 in several countries were also making important advances in the technic 

 of phase microscopy. 



The aim of this book is to present the results of these investigations 

 to the numerous microscopists engaged in scientific and technical work 

 so that they can advantageously apply phase microscopy to their wide 

 variety of problems. The possibilities of the phase method have been 

 found to be so extensive that we believe that practically every micros- 

 copist will find some suggestions in this book which will be of value. 



In presenting this material the authors have individually written the 

 various chapters. In each of these chapters the subject matter relates 

 to the specific type of investigation in which the author concerned has 

 been engaged. It is hoped that any resulting non-iniiformity in style 

 of presentation will be amply offset by a corresponding gain in authentic- 

 ity. The writer, however, being concerned with the more general aspects 

 and correlations of the problems of this subject, contributed Chapter I, 

 wherein is indicated the place of the phase method in the general scope 

 of microscopy. Another purpose of Chapter I is to give the reader a 

 simplified but basic insight into the optical principles involved in the 

 attainment of the results unique to phase microscopy. 



The section of this book relating to theory was prepared by Dr. 

 Harold Osterberg. The theoretical considerations given in Chapter II 

 provide the reader with a statement of the elementary theory of phase 

 microscopy. This material has been simplified so as not to be beyond 

 the ability of the reader of moderate mathematical attainment, yet it is 

 intended to be sufficiently precise to be of use to the microscopist who 

 wishes to gain a theoretical understanding of the principles involved in 



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