The Solar Activity 1833-1900. 



299 



the period, but the critical epochs of his cycle, completely harmonise 

 with those found in the present discussion of the sunspot and magnetic 

 curves. 



To illustrate more fully this connection, and to take only one case, 

 namely, rainfall, the three rainfall curves* are reproduced in fig. 2 

 (curves E, F, G). 



E and F represent the secular variations for what Professor 

 Bruckner calls " Eegulare Gebiete I und II,"f while curve E is the 

 mean for the whole set of observations he has employed, and 

 represents the secular variation of rainfall over the whole earth as 

 far as can be determined. 



The comparison of these curves with those representing the sunspot 

 and magnetic results given above them, shows that when the epoch of 

 maximum spotted area (curve B) follows late after the preceding 

 epoch of minimum (1843, 1878), or when the spotted area from 

 minimum to minimum is least (curve D), the long-period rainfall curve 

 is at its maximum or we have a wet cycle. 



When on the other hand the maximum (curve B) follows soon after 

 the preceding minimum (1867), and the spotted area for this cycle is 

 at a maximum (curve D), the rainfall curve is at a minimum or a dry 

 cycle is in progress. 



It may also be observed that in a detailed investigation of the 

 movements of glaciers, Professor Ed. Richter finds a cycle of thirty- 

 five years. In his 'History of the Variations of Alpine Glaciers,'! 

 he sums up his results as follows : — " Die Gletschervorstosse wieder- 

 holen sich in Perioden, deren Lange zwischen 20 und 45 Jahren 

 schwankt, und im Mittel der drei letzten Jahrhunderte genau 35 Jahre 

 betrug." 



Further he pointed out that the variations agreed generally with 

 Bruckner's climate variations, the glacier movement being accelerated 

 during the wet and cool periods. 



Another very interesting investigation to which reference must be 

 made is that which we owe to Mr. Charles Egeson, who published his 

 researches§ in solar and terrestrial meteorology just a few months 

 before the appearence of Professor Bruckner's volume. Mr. Egeson 

 not only finds a secular period of about thirty-three to thirty-four 

 years in the occurrence of rainfall, thunderstorms, and westerly winds 

 in the month of April for Sydney, but the epochs of maxima of the 

 two latter harmonise well with the epochs of the thirty-five yearly 

 period deduced in the present paper for sunspots. 



Thus he finds that the yearly numbers of days of thunderstorm 



* Bruckner, ibid., p. 171. 

 f Bruckner, ibid., p. 170. 



% ' Zeit. d. Deuts.-Oesterr. Alpen-Vereins,' 1891, Band 12. 

 § Egeson's 'Weather System of Sunspot Causality.' Sydney, 1889, 

 VOL. LXVIII. Y 



