68 Things not generally Known. 



at last to afford a view of the real solar surface of most intense 

 blackness. 



M. Schwabe, of Dessau, has discovered that the abundance 

 or paucity of spots displayed by the sun's surface is subject to 

 a law of periodicity. This has been confirmed by M. Wolf, of 

 Berne, who shows that the period of these changes, from mini- 

 mum to minimum, is 11 years and 1 1-hundredths of a year, 

 being exactly at the rate of nine periods per century, the last 

 year of each century being a year of minimum. It is strongly 

 corroborative of the correctness both of M. Wolf's period and 

 also of the periodicity itself, that of all the instances of the 

 appearance of spots on the sun recorded in history, even before 

 the invention of the telescope, or of remarkable deficiencies in 

 the sun's light, of which there are great numbers, only two are 

 found to deviate as much as two years from M. Wolf's epochs. 

 Sir William Herschel observed that the presence or absence of 

 spots had an influence on the temperature of the seasons ; his 

 observations have been fully confirmed by M. Wolf. And, from 

 an examination of the chronicles of Zurich from A.D. 1000 to 

 A.D. 1800, he has come to the conclusion "that years rich in 

 solar spots are in general drier and more fruitful than those of 

 an opposite character ; while the latter are wetter and more 

 stormy than the former." 



The most extraordinary fact, however, in connection with 

 the spots on the sun's surface, is the singular coincidence of 

 their periods with those great disturbances in the magnetic 

 system of the earth to which the epithet of " magnetic storms" 

 has been affixed. 



These disturbances, during which, the magnetic needle is greatly 

 and universally ao-itated (not in a particular limited locality, but at one 

 and the same instant of time over whole continents^ or even over the 

 whole earth), are found, so far as obsei-vation has hitherto extended, 

 to maintain a parallel, both in respect of their frequency of occui-rence 

 and intensity in successive years, with the abundance and magnitude 

 of the spots'in the same years, too close to be regarded as fortuitous. 

 The coincidence of the epochs of maxima and minima in the two series 

 of phenomena amounts, indeed, to identity; a fact evidently of most 

 important significance, but which neither astronomical nor magnetic 

 science is yet sufficiently advanced to interpret. Herschel 's Outlines. 



The signification and connection of the above varying phe- 

 nomena (Humboldt maintains) can never be manifested in their 

 entire importance until an uninterrupted series of representa- 

 tions of the sun's spots can be obtained by the aid of me- 

 chanical clock-work and photographic apparatus, as the result 

 of prolonged observations during the many months of serene 

 weather enjoyed in a tropical climate. 



M. Schwabe has thus distinguished himself as an indefatigable ob- 

 server of the sun's spots, for his researches received the Royal Astrono- 



