x PREFACE 



I here desire to express my indebtedness to these helpers for their 

 valuable services. My colleague, J. N. Finlayson, Professor of 

 Civil Engineering, kindly came to my aid in making the calculations 

 concerned with the kinetics of the Sphaerobolus gun. Once again 

 Mr. W. B. Grove, M.A., has been good enough to give me the benefit 

 of his assistance in reading the proofs. 



A. H. REGINALD BULLER. 



Kew, October 31, 1933. 



