CHAP, in.] ELECTRICITY AND MAGNETISM. 



159 



force. If the circuit is fixed and the magnet movable, 

 then the force acting on the magnet will also be such as to 

 tend to make the number of lines of force that pass 

 through the circuit a maximum (see also Art. 317). 



194. De la Rive's Floating Battery. The pre- 

 ceding remarks may be illustrated experimentally by 

 the aid of a little floating battery. A plate of zinc and one 

 of copper (see Fig. 87) are fixed side by side in a large 



Fig. 87. 



cork, and connected above by a coil of covered copper wire 

 bent into a ring. This is floated upon a dish containing 

 dilute sulphuric acid. If one pole of a bar magnet be 

 held towards the ring it will be attracted or repelled 

 according to the pole employed. The "floating circuit 

 will behave like the floating magnet in Fig. 44, except 

 that here we have what is equivalent to a floating 

 magnetic shell. If the S. pole of the magnet be pre- 

 sented to that face of the ring whicl) acts as a S. -seeking 

 pole (viz. that face round which the current is flowing 



