CHRONOLOGY DOUGLASS AND AXTEVS 305 



making contact- with botany and its associated sciences, with meteor- 

 ology, and especially climatology and astronomy ; with anthropology, 

 geology, and mathematics. 



At the outset I wish gratefully to acknowledge my obligation to 

 the Carnegie Institution for its important support of these clima- 

 tological studies since 1915. Especial thanks are expressed here to 

 the National Geographic Society, through whose valued assistance 

 the archeological material lias been obtained, which has carried south- 

 western climatic and historic records back to TOO A. D. The Amer- 

 ican Museum of Natural History assisted in the first collection of 

 prehistoric material. The Museum of Northern Arizona has given 

 great help in field work and laboratory space; C. G. White gave 

 funds for building the cyclograph ; the University of Arizona has 

 helped fundamentally by reducing teaching obligations; and now 

 the Kesearch Corporation of New York, through the Smithsonian 

 Institution, has contributed its generous and highly appreciated 

 award, for which encouragement I hereby express my sincere 

 gratitude. 



ORIGIN OF RESEARCHES 



Tlie stud}^ of tree rings began in 1001 as an astronomical investi- 

 gation based on the hypothesis that the sun affects weather and 

 weather affects trees, hence there is expectation of finding a history 

 of sun-spot variations in the annual rings of trees. This is especially 

 likely in a cool, dry climate like that of northern Arizona, where 

 moisture is vital to all vegetation and where winter gives annually 

 an emphatic resting period in the life of each tree. By 1913 precise 

 dating of rings had been established and a new method of analysis 

 had disclosed long-continued sequences of what ap})eared to be the 

 11-year solar cycle in the pines of Arizona. The failure of this 

 sequence from about 1G70 to 1720 caused serious questioning of its 

 reality. The results, however, were published in 1919, with mention 

 of this failure. But three jeavs later Dr. E. Walter Maunder, of 

 the Royal Observator}^, Greenwich, communicated his work on the 

 historical study of sun spots, from which he deduced a great dearth 

 of them from 1C45 to 1715. This dearth coincides closely with the 

 faihire of tlie trees to show this cycle. 



While this cycle in the Arizona pines was evident and sometimes 

 conspicuous, it was accompanied by other cycles, often of equal and 

 sometimes of superior importance. For years this was puzzling and 

 it was only in the end of 1926 that the possible relation of these other 

 cycles to the sun-spot cycle was discovered, as will be mentioned 

 below. 



