iv PEEFACE 



the mechanics of materials, and that a graphical method is given for 

 determining the gravity axis and moment of inertia of any plane area. 



In the treatment of curved pieces, such as hooks, links, and springs, a 

 simple graphical method of analysis is developed, which, it is believed, 

 is the only rigorous and at the same time simple general treatment 

 of the subject which has yet appeared in any American text-book. 



Many of the subjects treated in Part I, such as influence numbers, 

 the principle of least work, arched ribs, etc., are not found in other 

 American text-books of this grade. Such subjects have been uni- 

 formly reserved for the latter part of each chapter, and are preceded 

 by a footnote to the effect that they may be omitted if desired. 1\ 

 this means it is thought that the book may also be easily made ava li- 

 able for architectural students, or for others of whom little math- 

 ematical preparation is required, and who have only a brief time 

 allotted for the study of the subject. 



In Part II the chief feature is the increase in scope over similar 

 works, as indicated by the inclusion of separate chapters on it-enforced 

 concrete, timber, rope, cable, wire, and belting. 



In preparing this part the chief aim has been to guide the stu- 

 dent in his selection and use of the vast amount of information 

 now available on the physical properties of materials. With -this in 

 mind, only essentials have been given, and care has heen taken that 

 the book should not be overloaded with information seldom used. 

 The problems have been so chosen as to illustrate the text, and also 

 insure a thorough knowledge on the part of the student of that por- 

 tion of the subject under consideration. A special effort has ! -en 

 made to present the subject in a clear and concise form, so a> to 

 make it easily understood by a junior in engineering work, and, at 

 the same time, to render it interesting and inspiring as well 



As a consistent and uniform notation is an essential feature of any 

 scientific work, care has been taken that' each letter or symbol shall 

 have, so far as possible, but one signification. For convenience of 

 reference a tabulated statement of the notation is given immediately 

 after the table of contents, with references to those articles in which 

 each symbol is defined or used in a representative manner. 



THE AUTHORS 

 JULY, 1906 



