PREFACE vii 



The author desires to make grateful acknowledgment 

 to the following individuals, manufacturers, and depart- 

 ments of the United States Government, who have so 

 materially assisted in collecting the illustrative material : 

 Professor McAdie, Blue Hill Observatory, Readville, 

 Mass. ; H. A. Hutchins ; Dr. J. A. Bownocker ; The 

 Philadelphia Museums ; The Warner and Swasey Com- 

 pany ; Prest-o-Lite Company ; Cutler Hammer Manu- 

 facturing Company; Niagara Falls Power Company; 

 H. Koppers Company ; Landers-Frary Company ; Davey 

 Tree Expert Company; Chicago, Milwaukee and St. Paul 

 Rail Road ; A. I. Root Company ; Wright-Martin Com- 

 pany ; Swift and Company ; U. S. Navy Department ; 

 Bureau of Standards, Washington, D. C. ; U. S. Geologi- 

 cal Survey; U. S. Weather Bureau; U. S. Department 

 of Agriculture ; U. S. Reclamation Service ; Forest Serv- 

 ice, Washington, D. C. ; Ohio Agricultural Experiment 

 Station. 



C. H. L. 



