44 H. I. JENSEN. 



then at minima periods of sunspots. Out of thirty-eight 

 groups he found that seventeen occurred at maxima and 

 seventeen at minima, the remaining four being intermediate. 

 As unfortunately I have not been able to consult the 

 papers of these four authorities, I have had to rely on 

 Milne's " Earthquakes " for this information. Milne and 

 all subsequent writers on this topic, reject the opinions of 

 Kluge and Poey, on the ground of insufficient evidence. 

 Lapparent and other modern writers on geology, do not 

 even touch upon the question. 



Undoubtedly the conclusions contradict one another. 

 The latter investigations of Schmidt proved Wolf to be 

 wrong. Poey shows that earthquakes occur both at maxima 

 and minima, which certainly is so, but Kluge alone tries to 

 demonstrate that they predominate at sunspot minima. 

 Here it will be necessary to point out that if the results of 

 these investigators are contradictory, it is not to be 

 marvelled at, considering that we have no great abundance 

 of information on sunspots before 1833, that the sunspot 

 period may vary from nine to thirteen years, and that the 

 dates of maxima and minima before that time have been 

 obtained by calculation from a formula which may yet be 

 shown to be incorrect. At the present time we have more 

 data, sunspots have been closely observed for the last sixty 

 or seventy years, and those who desire to see the exact 

 sunspot curve from 1834 to the present, may find it in a 

 paper by W. J. S. Lockyer. 1 



The sunspot curve on my chart is the one constructed 

 by Mr. H. O. Russell from observations conducted in India. 

 It does not show all the variations, ups and downs, that 

 actually take place, but is made by joining the years of 

 maximum and minimum sunspot activity by straight lines. 

 Now, on looking at Plate II., we must not suppose that the 



1 Monthly Notices of the Koyal Astronomical Society, Dec. 13, 1901. 



