4 PREFACE 



through the chapter, and giving valuable criticism and 

 advice. 



To Mr. Dean, late of the Delta Works, Greenwich, 

 my thanks are due for reading the chapter on ' Metals ', 

 and to many other persons for permission to reproduce 

 drawings and photographs. 



A list of the chief authorities and books of reference 

 will be found at the end of Part II. 



The numerous statistics which occur have been inserted, 

 not so much as being valuable in themselves, but in 

 order to support general statements and to give point 

 to such phrases as 'much' and 'little', 'great' and 

 * small '. 



J. CLINTON CUNNINGHAM. 

 GREENWICH. 

 March 1920. 



