150 SMITHSONIAN xMISCELLANEOUS COLLECTIONS VOL. 70 



summer heat than with the greater winter cold, the relation which he 

 found, if it exists, can only be explained by increased solar radiation 

 at the time of sun spot minimum. 



Dr. Hahn (1877) has shown that for Leipsic the difference of 

 the absolute yearly extremes of the temperature varies directly as 

 the sun spots. This is completely confirmed by Liznar (1880) by 

 observations at eight other stations in Europe. In the years of sun 

 spot maxima occur the highest temperature maxima and the lowest 

 minima, while in years of sun spot minima the relation is inverted. 

 (Compare Hann 1908, p. 358). Liznar also investigated the tem- 

 perature variations at thirteen stations, among these St. Petersburg, 

 Calcutta, and Hobart (Tasmania), and found for all some agree- 

 ment with the eleven-year sun spot periods. For Vienna, Prague, 

 Tuschaslau, Briinn, and Trieste, 1857 to 1870, he found that the 

 mean of the daily amplitude was smallest in the years 1859 and i860, 

 and 1870-71, at sun spot maximum, while the greatest daily ampli- 

 tude occurred about two years from the sun spot minimum. This 

 was accordingly exactly opposite to what he found for the yearly 

 range of temperature. 



Unterweger (1891) believed that he found a short period of 

 between 26 and 30 days in the sun spots and in the solar activity. 

 This period while not produced by the rotation of the sun yet was 

 influenced by it and occurred in the average in 29.56 (±0.5) days. 

 Further, he found a period of 69.4 days fairly strongly developed 

 and besides this various others less distinct. In a review of Unter- 

 weger 's investigations Koppen thinks (1891) that he has confirmed 

 the existence of such short periods but he did not obtain the same 

 values of their duration as those of Unterweger. 



Frank H. Bigelow found (1894) a periodicity in the variations 

 of the terrestrial forces as measured in Europe, in correlation 

 with the rotation period of the sun. The period was computed to 

 be 26.68 days, so that, for example, discernible minima in the ter- 

 restrial magnetic forces occurred on the first to second, fifth, ninth, 

 fifteenth, twentieth, and twenty-fourth day of each rotation, while 

 on the other hand the maxima occurred on the third, seventh, eleventh 

 to fourteenth, sixteenth to nineteenth, twenty-second, and twenty- 

 sixth days.^ 



^ One detects here what Bigelow seems scarcely to have noticed, indications 

 of a fourteen-day period, since from thirteen to fifteen days after each mini- 

 mum or maximum a corresponding minimum or maximum appears, which 

 therefore corresponds to the opposite side of the sun. 



