vi PREFACE 



hearty cooperation of manufacturers and business men and the 

 interest they have manifested in our efforts to present faith- 

 fully the application of science to the actual affairs of life 

 have been most helpful. Chapter IV, The Weather, is pub- 

 lished with the approval of the Central Office of the United 

 States Weather Bureau. 



THE AUTHORS. 

 NORMAL, ILLINOIS. 

 May 20, 1916. 



