302 POGGENDORFF ON CLOSED ELECTRO-MAGNETS. 



Such a ring, uniformly magnetized all round, represents a 

 magnet without a pole, which produces no external effect ; in 

 the act of magnetizing, nevertheless, it shows the same phaeno- 

 mena of induction as a horse-shoe magnet and its keeper. The 

 author convinced himself of this by coiling two insulated wires 

 round the same ring of iron, one of which was connected with 

 the galvanic battery, and the other with the induction-galvano- 

 meter. 



Similar rings or tubes of small dimensions might perhaps be 

 made use of for very interesting experiments on frictional 

 electricity. 



[J. T.] 



