PREFACE vii 



has been made by the authors to follow an encyclopaedic plan, under 

 which all fields should receive proportional space and treatment, 

 each by a competent representative, but some fullness of presenta- 

 tion has been aimed at in the particular branches with which they 

 are themselves familiar, with briefer indication of developments 

 along other lines. 



The authors gladly acknowledge their indebtedness to mafty 

 men of science interested in their undertaking, and to the special 

 histories already referred to, on which their own work is largely 

 based. Many brief typical quotations from the more important 

 authorities are given as a basis for wider or more special study, 

 but no systematic attempt has been made to examine original 

 sources. No one can possibly be more aware than are the authors 

 of the shortcomings of their work, and corrections of errors, from 

 which a book of this kind cannot hope to have escaped, will be 

 welcomed. 



MASSACHUSETTS INSTITUTE OF TECHNOLOGY, 

 CAMBRIDGE, 1917. 



