156 PHYSICAL GEOGRAPHY OF THE SEA, AND ITS METEOROLOGY. 



346. Lines of magnetic force. — This eminent philosopher has 

 also shown that if you place a magnetized bar of iron on a smooth 

 surface, and sift fine iron filings down upon it, these filings will 

 arrange themselves in curved lines as in Fig. 1 ; or, if the bar he 

 broken, they will arrange themselves as in Fig. 2. The earth it- 

 self, or the atmospheric envelope by which it is surrounded, is a 

 most powerful magnet, and the lines of force which proceed 

 whether from its interior, its solid shell, or vaporous covering, 



FijT. 1. 



""''""''"■'■ Fig. 2. 



are held to be just such lines as those are which surround arti- 

 ficial magnets ; proceed whence they may, they are supposed to 

 extend through the atmosphere, and to reach even to the plane- 

 tary spaces. Many eminent men and profound thinkers, Sir 

 David Brewster among them, suspect that the atmosphere itself 

 is the seat of terrestrial magnetism. All admit that many of 

 those agents, both thermal and electrical, which play highly 

 important parts in the meteorology of our planet, exercise a 

 marked influence upon the magnetic condition of the atmosphere 

 also. 



347. TJie magnetic influences of the oxygen of tlie air and of tin 

 sj)ots on the sun. — Now, when, referring to Dr. Faraday's dis- 

 covery (§ 345), and the magnetic lines offeree as shown by the 

 iron filings (§ 346), we compare the particles of oxygen gas to 



