BUTTERWORTH PUBLICATIONS LTD 



BELL YARD . TEMPLE BAR . LONDON . W.C.2 



BUTTERWORTH & CO (AFRICA) LTD . DURBAN 

 BUTTERWORTH & CO (AUSTRALIA) LTD . SYDNEY 

 MELBOURNE . BRISBANE . WELLINGTON . AUCKLAND 

 BUTTERWORTH & CO (CANADA) LTD . TORONTO 



U.S.A. Edition published by 



ACADEMIC PRESS INC., PUBLISHERS 



125 EAST 23rd STREET 



NEW YORK 10, NEW YORK 



First Edition January 1952 



Set in Baskerville type 

 Printed in Great Britain by J. W. Arrowsmith Ltd., Bristol 



