95 



TABLE I. 

 Schwabe's Observations of Solak Spots. 



[Kirkwood. 



(4.) This table presents a very marked periodicity ; the interval be- 

 tween two consecutive maxima or minima, being, according to Schwabe, 

 about 10 years. Soon after the announcement of this interesting dis- 

 covery Dr. Lamont, of Munich, detected a corresponding decennial 

 period in the variation of the magnetic needle ; the epochs of maxima 

 and minima in the latter coinciding with those in the former. These 

 i-esults have also been confirmed by other observers in places quite 

 remote from each other ; so that the decennial magnetic cycle may be 

 regai'ded as well established. The equality of this period with that of 

 the solar sjDOts naturally suggested the hypothesis of their intimate rela- 

 tionship. Such a causal connection may be difficult of explanation : the 

 fact, however, is placed beyond doubt by the researches of Wolf and 

 Sabine.* The former, besides carefully observing the sun-spots since 



* These magnetic variations, wliicli will not be discussed in the present paper, are mentioned to 

 give completeness of view to the phenomena under consideration. It is also worthy of remark 

 that the Aurora Borealis is believed to exhibit a corresponding periodicity. 



