CHAP, v.] ELECTRICITY AND MAGNETISM. 299 



aside by a magnet, or caused to rotate around a magnet- 

 pole. The " brush " discharge when taking place in a 

 strong magnetic field is twisted. The voltaic arc (Art. 

 371) also behaves like a flexible conductor, and can be 

 attracted or repelled by a magnet. Two stationary 

 positively electrified particles repel one another, but two 

 parallel currents attract one another (Art. 332), and if 

 electrified particles flowing along act like currents, there 

 should be an (electromagnetic) attraction between two 

 electrified particles moving along side by side through 

 space. According to Maxwell's theory (Art. 390) the 

 electrostatic repulsion will be just equal to the electro- 

 magnetic attraction when the particles move with a 

 velocity equal to the velocity of light. 



Quite recently Hall has discovered that when a 

 powerful magnet is made to act upon a current flowing 

 along in a strip of very thin metal, the equipotential 

 lines are no longer at right-angles to the lines of flow of 

 the current in the strip. This action appears to be 

 connected with the magnetic rotation of polarized light 

 (Art. 387), the co-efficient of this transverse thrust of 

 the magnetic field on the current being + in gold, and 

 in iron. 



338. Ampere's Theory of Magnetism. Ampere 

 finding that solenoids (such as Fig. 1 1 6) act precisely as 

 magnets, conceived that all magnets are simply collections 

 of currents, or that, around every individual molecule of 

 a magnet an electric current is ceaselessly circulating. 

 We know that such currents could not flow perpetually 

 if there were any resistance to them, and we know that 

 there is resistance when electricity flows from one mole- 

 cule to another. As we know nothing about the interior 

 of molecules themselves, we cannot assert that Ampere's 

 supposition is impossible. Since a whirlpool of electricity 

 acts like a magnet, there seems indeed reason to think 

 that magnets may be merely made up of rotating portions 

 of electrified matter. 



