NO. 4 TEMPERATURE VARIATIONS IN THE NORTH ATLANTIC I79 



greater regularity. In the longer periods the two maxima follow 

 the precipitation most closely (one to two years) after the sun spot 

 extremes ; the minimum, however, some years later. The correspond- 

 ing extremes of the water level and the temperature come about a 

 year later than that of the precipitation, but the temperature is 

 again more irregular than the water level (see Johansson, 1912). 



In a later article (1913) Wallen has exhaustively studied many 

 years of variations of water level at Malaren, the precipitation in 

 Upsala and the air temperature at Stockholm in a similar way to 

 that of his earlier paper of 1910. For the shorter period he finds: 



Temperature, Stockholm. Length of period 26 months, Amplitude 2.8° C. 

 Precipitation, Upsala. Length of period 24 months, Amplitude 20 mm. per 



month. 

 Water level Malaren. Length of period 30 months. Amplitude 40 cm. 



The eleven-year period in all three cases is double featured as 

 Wallen had found for the height of the water at Wenern. The two 

 maxima in the height of the water in Malaren are about equally 

 great. The first maximum comes about fifteen months and the other 

 eight months after the sun spot minimum. The amplitude is about 

 20 cm. For the precipitation at Upsala the difiference between the 

 two maxima is considerable, while the two minima are about equally 

 intense. The extremes come some months earlier than the cor- 

 responding extremes in the water level, and the amplitude in the 

 monthly values of the precipitation amounts on the average to 

 12 mm. Both for the precipitation and for the air temperature Wal- 

 len found similar three-year and eleven-year variations for other 

 stations in north Europe, as well as fo'r Upsala and Stockholm. He 

 also found distinct traces of the Briickner period in these elements in 

 Sweden. 



GROWTH OF TREES 



We must now refer to an interesting investigation of Prof. A. E. 

 Douglass (1914). By accurate measurements of the rings of yearly 

 growth of pines (Pinus ponderosa) in Arizona, and by careful com- 

 parison of the values found with the measured precipitation in this 

 region in the last century, he conceives that he has established a 

 basis whereby he can determine the variations in the precipitation 

 in Arizona for the last five hundred years, employing for this pur- 

 pose the measurements of the yearly growth for a number of selected 

 and very old trees. In this manner he has obtained curves for the 

 growth of the trees and for the precipitation in this interval of time. 



