viii PREFACE 



the application of the phase microscope. In addition. Chapter II will 

 guide the microscopist in selecting those instrumental conditions which 

 provide the most efficient results under a wide variety of conditions of 

 the microscopic specimen. 



In the Appendix (Chapter VII) Dr. Osterberg presents a detailed 

 mathematical treatment of the diffraction theory of image formation 

 in the phase microscope when used in conjunction with the commonly 

 used Kohler method of illumination. This diffraction theor}^ is treated 

 in its entirety in the Appendix because it is a subject in which the special- 

 ist in physical optics rather than the microscopist will probably be 

 chiefly interested. 



The instrumentation necessary for the application of phase micros- 

 copy is described by Dr. Helen Jupnik in Chapter III. The functions 

 and properties of the various elements of the phase microscope are 

 described. An important part of this chapter from the point of view of 

 the microscopist is the description of the necessary alignment and 

 adjustment of the microscope so that the most satisfactory and meaning- 

 ful images can be obtained. The comparison of the salient features of 

 the phase microscope equipment supplied by different manufacturers 

 indicates the substantial progress which has been made by these manu- 

 facturers in their efforts to provide the microscopist with suitable, 

 adequate, and available instrumentation. The most recent technics, 

 marking the borderline between commercially available and non- 

 available equipment, are described in the latter part of Chapter III. 

 This material is intended to give the reader an idea of the present 

 frontier of developments. 



Chapters IV, V, and VI were written by Dr. Oscar W. Richards, who 

 has made an extensive investigation of the applications of phase micros- 

 copy in the fields of biology, medicine, and industry. These chapters 

 deal comprehensively with the practice of phase microscopy, and illus- 

 trate by numerous and typical examples the wide extent of successful 

 applications of the phase procedure. For these examples the older 

 microscopic methods are found to be insufficient. 



The great quantity of research work relating to the subject of phase 

 microscopy since its comparatively recent inception is shown by the 

 extensive bibliography. 



During the course of their phase microscope investigations, extending 

 over a period of nine years, the authors have fortunately received 

 suggestions and active encouragement from so many people that it is 

 impossible to express here our deep gratitude to all of them individually. 

 In particular, we wish to acknowledge with thanks the kind cooperation 

 of Dr. George O. Gey, of the Johns Hopkins School of Medicine, who 



