PREFACE 



between them produced an unblemished typescript from a far-from- 

 perfect manuscript ; the Staff of the Liverpool University Library 

 (especially Miss E. Whelan) went to considerable trouble to trace and 

 obtain obscure journals and monographs. 



My greatest debt of gratitude is, however, due to Professor R. A. 

 Morton, F.R.S. His encouragement stimulated me to begin this book 

 and his continued unstinting help during the writing of it has been 

 invaluable. 



Conditions in the British publishing world are today extremely 

 difficult and the long delays in publishing Scientific Books, especially 

 monographs, tend to make them out of date before they appear. My 

 Publishers have been most tolerant in dealing with my attempts to 

 reduce this delay to a minimum. It is entirely due to their whole- 

 hearted co-operation, that it has been possible eventually to include 

 information available in this country up to the end of September 1951. 



T. W. G. 



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