ADVANCE OF ASTRONOMY. 205 



William HerschePs picture of the sun seems to 

 have been generally accepted for about seven decades. 

 His son, Sir John Herschel, while working at the 

 Cape, was probably beginning to doubt its validity 

 when he maintained that the sun's rotation was inti- 

 mately concerned with the formation of sun-spots; 

 and the attention which he, Baily, Airy, Arago, 

 Struve, and others paid to the corona, chromosphere, 

 and other luminous appendages of the sun observed 

 during the eclipses of 1842 and 1857, led to further 

 suspicions. 



The careful patience of an amateur Heinrich 

 Schwabe (d. 1875) made the next step possible, 

 for by the observations of a quarter of a century he 

 showed, about 1850, that there was a periodicity in 

 the appearance of sun-spots. But this, in itself in- 

 teresting, acquired additional importance when the 

 magnetic observations which the enthusiasm of Hum- 

 boldt, Gauss, and others had secured in five conti- 

 nents led Dr. John Lament and Sir Edward Sabine 

 (1852) independently to the conclusion (based on 

 different sets of data), that there was a remarkable 

 harmony between periods of disturbance in terrestrial 

 magnetism and the periods of the sun-spots. The 

 congruence was confirmed in the same year (1852) 

 by Rudolph Wolf and by A. A. Gautier, and although 

 Sir William Herschel's association of the price of 

 bread, periods of sunny weather, and frequency of 

 sun-spots was not borne out, the influence of the sun 

 on the earth's magnetism was henceforth recognized 

 as a fact. 



It is now generally believed that the sun is sur- 

 rounded by a halo of incandescent clouds the photo- 

 sphere outside of which there is a solar atmosphere 

 composed of vapours of hydrogen, calcium, iron, and 



