ted in their writings. The reader will thus find that the authors often cut 

 across fields and the discussant, when confronted by inclusive ideas of the au- 

 thor , must often respond by giving record to his own solution. 



Finally, the editors would like to express their gratitude to the many 

 members of their own fellow institutions and the National Research Council, who 

 have rendered invaluable assistance in preparing the manuscript for publication. 

 Our inability to list all the names of those who aided in preparation of illustra- 

 tions, compiling the index, checking references, typing and retyping and the 

 many other necessary tasks in no way should be taken as a lack of appreciation 

 for the significance of their contribution. Without their effective and unreward- 

 ed help this report would not be available. 



John D. Isaacs 

 Columbus O'D. Iselin 



VI 



