VI PREFACE 



seed grading- and cleaning machinery, cotton machinery, 

 potato machinery, garden machinery, and other classes. 

 The amount of information at hand concerning these 

 classes of machinery did not justify their inclusion. Farm 

 Motors has been made more complete, but some of the 

 motors used to a limited extent in agricultural practice, 

 as hot-air engines and water-wheels, have been omitted. 

 Although electrical machinery is not much used in agri- 

 culture, its use is increasing and the interest in the sub- 

 ject has been so general that a chapter on the same has 

 been included. As the efficiency and life of farm 

 machinery depends largely upon the way and manner it 

 is repaired, a short chapter on the Farm Workshop has 

 been added. 



To make instruction in Farm Machinery and Farm 

 Motors efficient it should in all cases be supplemented 

 with laboratory and field instruction, and it is not the 

 purpose of this book to displace such instruction. 



An attempt has been made to make the material practi- 

 cal, useful and helpful, and although written primarily 

 for a text book, it is hoped that it will be useful to many 

 engaged in practical work. 



The authors know that their attempt to prepare a text 

 book has not been perfect, and not only will errors be 

 found in the subject matter, but the material will lack 

 pedagogic form in places. Any criticism or suggestions 

 in these respects will be duly appreciated. The authors 

 wish also to acknowledge the obligations they owe many 

 friends for suggestions and aid in many ways. Thanks 

 are due the publishers for their work in preparing the 

 illustrations, which at first seemed to be an almost end- 

 less task. 



J. B. DAVIDSON. 

 L. W. CHASE. 



