l62 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 70 



same as found by Wallen for Karlstad-\'anersborg-. Variations of 

 temperature in Helsingfors were found in winter with periods of 

 3.0 years and in summer with 2."] and for the year 2.9 years. Ac- 

 cording- to Johansson it is very clear " that this short period variation, 

 particularly for the winter, depends on the water temperature of the 

 northern ocean (see also the results of Pettersson and Meinardus)." 

 This conclusion must be understoo'd in this way. that the air tempera- 

 ture in Helsingfors and the water temperature at the Norwegian 

 lighthouses (not in the North Sea) show the same variation, so that 

 the variations in temperature not only for Norway and Sweden, 

 but also for Finland or parts of it are found in common. 



In his paper on volcanic dust and climatic variations, Humphreys 

 (1913) discusses yearly mean temperatures for the period 1872 to 

 1912, for seventeen stations in the United States, seven stations in 

 Europe and one station in India. He has chosen stations which 

 have considerable height above the sea. Most of them lie between 

 2,000 and 10,000 ft. elevation. The variations in these mean tem- 

 peratures he has, like Abbot and Fowle (1913), compared with the 

 variations in the number of sun spots, the variations in the measured 

 solar radiation at the earth's surface as observed by the pyrhelio- 

 meter, and also with the volcanic eruptions on the earth. He finds 

 excellent agreement, and when he continues the combined curve for 

 sun spots and pyrheliometric values at the earth's surface of Abbot 

 and Fowle to the year 19 13, he obtains a yet more convincing im- 

 pression of agreement between this curve and the curve for the 

 terrestrial temperature. He traces the curve of terrestrial tempera- 

 ture backwards to 1750 and compares it with the inverted sun spot 

 curve and also with the recorded volcanic eruptions. While the two 

 curves for temperature and sun spots show many dissimilarities, 

 there appears to be a close correspondence between the years of 

 low temperatures such as 1767, 1785, 1813 to 1816 and others, and 

 the recorded violent volcanic eruptions. Humphreys comes there- 

 fore to the same conclusion as Abbot and Fowle, namely, that the 

 variations in the temperature at the earth's surface are partially 

 dependent on variations of solar activity which have the eleven- 

 year or sun spot period and partly on the volcanic dust in the atmos- 

 phere of the earth. In consequence of the small diameter of the 

 particles of the volcanic dust, it would have the tendency to diffusely 

 reflect rays of short wave length like visible solar rays in a high 

 degree, but rays of great wave length, such as those emitted by the 

 earth's surface, would be freely transmitted. Hence the incoming 



