CH. xxxvi. SUN-SPOTS AND MAGNETISM. 379 



metals and earths, and is always turning round from west to 

 east, so that one part after another comes under the heat of 

 the sun, and is made hotter than the rest. Therefore, since 

 an electric current tends to flow round the circuit when the 

 functions of two different metals are kept at different temp- 

 eratures, it has been suggested that this may cause the 

 electric currents to flow round from east to west, as they 

 did through the metals in Seebeck's stirrup, thus inducing 

 lines of magnetic force from north to south. There may, 

 however, be some closer connection between the sun itself 

 and magnetic action (see p. 381). 



Spots on the Sun, and their effect on the Earth's 

 Magnetism, Schwabe and Sabine, 1825-1859. It was 

 mentioned at p. 90 that Galileo and other astronomers of 

 the seventeenth century first observed that from time to 

 time dark spots appear on the face of the sun. These 

 spots were much studied by the astronomers who came 

 after Galileo ; but Sir William Herschel was the first to 

 suggest, in 1793, that they were caused by the opening of 

 bright luminous clouds which float round the sun, and 

 break away sometimes in one place and sometimes in 

 another, allowing us to see down through the gap into the 

 body of the sun itself, which has thus the appearance of a 

 dark spot. This is the explanation now received by astro- 

 nomers as most probable, and it accounts for the constant 

 appearance and -disappearance of the spots. 



In the year 1826, a well-known German astronomer, 

 Herr Schwabe, of Dessau (who died in 1874), determined 

 to take regular notes of the periods when there were most 

 spots to be seen on the face of the sun. Every day during 

 twelve years, when the sky was clear enough for him to 

 observe the sun, he examined it through his telescope, and 

 noted how many spots he could see. 



