vm PREFACE 



individual opinions and organized the material in accordance with their 

 own thinking on the subject. One of our primary aims has been to present 

 constructive and suggestive viewpoints, and in so doing we have had to 

 run the risk of being in error. This risk could have been avoided by com- 

 piling an uncritical review with none of the reviewers' opinions expressed, 

 but to have done this would have effectively defeated the purpose of 

 the book. 



We wish to beg the indulgence of our readers for mistakes and imper- 

 fections that may be found, and if they are such as can be remedied in 

 later printings or editions we will appreciate having them called to our 

 attention. There has been some unavoidable duplication in different areas 

 of the discussion, but this has been retained whenever doing so would 

 contribute materially to the unity and understandability of the particular 

 section. In view of the magnitude of the task, which turned out to be even 

 greater than we had anticipated, and because the preparation of the 

 manuscripts had to be superimposed upon active research and/or teaching 

 programs, we hope that our readers will be charitable in judging the 

 product of our labors. 



It has not been feasible to synchronize our efforts completely and in 

 the respective sections the literature has not been completely reviewed 

 up to exactly the same date. Even within sections the up-to-dateness may 

 vary slightly from topic to topic. For example, the citation of individual 

 crucial papers up through April or May, 1950, does not mean that all of 

 the literature has been covered up to that point. We cannot hope that the 

 material which we have presented will remain up-to-date for long. Indeed, 

 a sincere desire to promote research is equivalent to hoping that this 

 volume will rapidly become out-of-date. But, like Professor Lewis, we 

 can hope that necessary changes will involve "matters of detail rather 

 than of essence." 



Roger J. Williams 

 Robert E. Eakin 

 Ernest Beerstecher, Jr. 

 William Shive 

 Austin, Texas 

 June 15, 1950 



