154 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. "JO 



A high pressure zone extends westward from Florida towards 

 northern California and Oregon which divides the United States 

 into two parts, so that he thinks the Pacific States are associated 

 with the tropical system and the influence on the temperature of 

 the United States is not directly an action of solar radiation, but 

 only indirectly called forth by the heat which is carried by hori- 

 zontal air currents. 



We have summarized so far the investigations of Bigelow, be- 

 cause they have many points of interest in connection with our 

 results, even though we dififer from him in some respects. 



In his well-known vv'ork on Climatic Variations since i/OO, 

 Bruckner (1900) treats of the secular variations of the tempera- 

 ture of the earth and compares them with the variations of air 

 pressure and rain fall. He finds a well-marked period of varia- 

 tion of these elements of approximately thirty-six years. By a 

 collection of observations on the ice condition of rivers, on the date 

 of the wine harvest and on the frequency of strong winds for 

 several hundred years, he determines this period exactly as 34.8 ± 

 0.7 years. The amplitude of the temperature variations within this 

 period " is in all parts of the earth approximately of equal magni- 

 tude at about 1° C." This is considerably greater than the ampli- 

 tude of the eleven-year period according to Koppen. Bruckner 

 finds that his secular climatic variation with the period of about 

 thirty-five or thirty-six years, has absolutely no connection with 

 the sun spot frequency." 



He concludes " there can be no doubt that the variations of the 

 temperature are the primary effects, variations of air pressure and 

 rain fall on the other hand secondary." The cause of the observed 

 terrestrial temperature variations according to his thought can be 

 sought in the oscillation of the heat coming in from the sun. In 

 years with stronger solar radiation, land in summer would be warm 

 to a greater degree, which would tend to produce relatively lower 

 air pressure over the land with respect to that over the ocean. In 

 winter it is, however, the reverse : for the land would be strongly 

 cooled by the outgoing radiation, while the ocean would retain an 

 excess of heat which is piled up during the summer, so that the 

 temperature difference between ocean and continent is again ab- 

 normally great, this time in favor of the ocean. Furthermore, the 

 air pressure dift'erence is also accentuated : the barometer stands 

 too low on the ocean, too high on the land. This intensification of 

 the winter anti-cyclone on the land can in its turn influence the 

 temperature by favoring the outgoing radiation. 



