Eight-Year Cycle in Relation to Physical Cause 107 



convince, mankind. For thirty years never has the 

 Sun exhibited his disk above the horizon of Dessau 

 without being confronted by Schwabe's unperturb- 

 able telescope, and that appears to have happened on 

 the average about 300 days a year. So, supposing that 

 he observed but once a day, he made 9000 observations, 

 in the course of which he discovered about 4700 groups. 

 This is, I beheve, an instance of devoted persistence 

 unsurpassed in the annals of astronomy. The energy 

 of one man has revealed a phenomenon that had eluded 

 even the suspicion of astronomers for 200 years!" 



Let us for a moment look more closely into Schwabe's 

 methods and results : 



(1) Length of his observations. He began his ob- 

 servations in 1826 and announced in 1843 his discovery 

 of a periodicit}^ of ten years. His observations of 18 

 years covered not quite two full periods of the phenome- 

 non. 



(2) Variability of the period. At the time Schwabe's 

 discovery received official recognition, February, 1857, 

 his observations covered just thirty years, or, assimiing 

 the period to be ten years, the length of three cycles. 

 In the very act of praising his work President Johnson 

 was prompted to say, "the exact period Schwabe does 

 not pretend to have determined. That it is liable to 

 perturbation is evident. During twenty-seven years of 

 the series, the results were extremely regular; during 

 the last three years they have shown symptoms of 

 disturbance. The epoch of minimum which consistently 

 with earlier indications should have happened in 1853, 

 did not occur until 1856." 



(3) Other coexistent cycles. As far as I am aware he 



