PREFACE IX 



photographs secured from the Nebraska Experiment Station 

 have also been used, Professor T. A. Kisselbach furnishing 

 several of these. Also the Portland Cement Co., Deere and 

 Co., Janesville Machine Co., Planet Jr. Co., and Sandwich 

 Manufacturing Co. have furnished illustrative material. 



E. G. MONTGOMERY. 



Ithaca, N.T., 

 January 1, 1913. 



