SUMMARY AND PREFACE 



tical form. So far as is possible, the main account and the 

 Appendix have been written in parallel to facilitate cross-reference. 



Since the reader will probably need cross-reference frequently, 

 the chapters have been subdivided into sections. These are 

 indicated thus : S. 4/5, which means Chapter 4's fifth section. 

 Each figure and table is numbered within its own section : Fig. 

 4/5/2 is the second figure in S. 4/5. Section-numbers are given 

 at the top of every page, so finding a section or a figure should be 

 as simple and direct as finding a page. 



Figs. 8/8/1 and 8/8/2 are reproduced by permission of the 

 Editor of Electronic Engineering. 



It is a pleasure to be able to express my indebtedness to the 

 Governors of Barnwood House and to Dr. G. W. T. H. Fleming 

 for their generous support during the prosecution of the work, 

 and to Professor F. L. Golla and Dr. W. Grey Walter for much 

 helpful criticism. 



W. ROSS ASHBY 



vn 



