VI PREFACE 



Johnson, that, "Other qualifications being equal, the more 

 advanced and complete the theory of which the farmer is the 

 master, the more successful must be his farming. The more he 

 knows, the more he can do. The more deeply, comprehen- 

 sively, and clearly he can think, the more economically and 

 advantageously can he work," and that "A true theory is the 

 surest guide to a successful practice." 



In short, the book is intended for the student rather than 

 directly for the farmer and assumes a certain degree of prelim- 

 inary training on the part of the reader, including an elementary 

 knowledge of chemistry and physics. 



The author is under obligations to The Honorable Secretary 

 of Agriculture, for permission to reproduce, in Chapter XVIII, 

 a part of Bulletin No. 459 of the United States Department of 

 Agriculture; to the Macmillan Company for the similar use in 

 Chapter XV of material from Bailey's "Cyclopedia of American 

 Agriculture"; and to Messrs. Henry and Morrison for permis- 

 sion to base the tables of the net energy values of feeding stuffs 

 contained in the Appendix upon their extensive compilations 

 in the fifteenth edition of "Feeds and Feeding." He is like- 

 wise indebted to the following publishers for the use of the cuts 

 named : 



The Carnegie Institution of Washington, Figure 24. 



The F. A. Davis Company, Figure 17. 



Ginn & Company, Figures 2, 3, 6, 7, 8, 16, 19, 20, and 22. 



The Macmillan Company, Figures 4, 15, 29, 31, 32, 33, 34, 

 37, 43, 44, and 45. 



The W. B. Saunders Company, Figures 1,5, and 14. 



John Wiley & Sons, Inc., Figures 18 and 40. 



STATE COLLEGE, PA., 

 May, 1917. 



