INTRODUCTION 7 



collection of prehistoric beams; to the Toll Roads Company and to 

 Dr. W. S. Adams, of the Carnegie Institution, for permission to collect 

 samples on Mount Wilson; to Mr. E. W. Griffith, of Las Vegas, 

 Nevada, for a trip to the Charleston Mountains; to Mr. N. P. Wheeler, 

 jr., for the trip and collection of white pines near Endeavor, in north- 

 western Pennsylvania; to the forest supervisor at Klamath Falls, 

 Oregon, and Mr. Emanuel Fritz, for collections in Oregon and northern 

 California; to the directors and curators in the American Museum, 

 the Metropolitan Museum, and the Museum of the American Indian, 

 New York; Peabody Museum, Cambridge; National Museum, Wash- 

 ington; and the Field Museum, Chicago, for cooperation and help 

 in measuring specimens; and especially to Dr. John C. Merriam, 

 President, and Dr. F. E. Clements, ecologist, of the Carnegie Institu- 

 tion, for their continued help and interest in this line of investigation. 



PREVIOUS WORK 



The first publication by the author was in 1909, in the Monthly 

 Weather Review. This was followed by other articles until the whole 

 was summarized in 1919 in a volume with the same title as the present 

 one and published under the same auspices. At that time identifica- 

 tion and measurement had been made of about 75,000 rings in some 

 230 different trees from the States of Oregon, California, Arizona, 

 Colorado, and Vermont, as well as from England, Norway, Sweden, 

 Germany, and Bohemia (near Pilsen). That volume dealt with 

 studies upon the yellow pine about Flagstaff, Arizona, climatic con- 

 ditions there, the yearly identity of rings, cross-identification, time 

 of year of ring formation, number of trees necessary, the actual collec- 

 tion of yellow and Scotch pine and sequoia samples, methods of 

 curve production, correlation with rainfall and with solar activity, 

 and cycles and methods of determining them. The present book 

 opens with the development of technique in collecting and treating 

 specimens. 



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